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Glyphosate, Hard Water and Nephrotoxic Metals: Are They the Culprits Behind the Epidemic of Chronic Kidney Disease of Unknown Etiology in Sri Lanka?


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The current chronic kidney disease epidemic, the major health issue in the rice paddy farming areas in Sri Lanka has been the subject of many scientific and political debates over the last decade. Although there is no agreement among scientists about the etiology of the disease, a majority of them has concluded that this is a toxic nephropathy. None of the hypotheses put forward so far could explain coherently the totality of clinical, biochemical, histopathological findings, and the unique geographical distribution of the disease and its appearance in the mid-1990s. A strong association between the consumption of hard water and the occurrence of this special kidney disease has been observed, but the relationship has not been explained consistently. Here, we have hypothesized the association of using glyphosate, the most widely used herbicide in the disease endemic area and its unique metal chelating properties. The possible role played by glyphosate-metal complexes in this epidemic has not been given any serious consideration by investigators for the last two decades. Furthermore, it may explain similar kidney disease epidemics observed in Andra Pradesh (India) and Central America. Although glyphosate alone does not cause an epidemic of chronic kidney disease, it seems to have acquired the ability to destroy the renal tissues of thousands of farmers when it forms complexes with a localized geo environmental factor (hardness) and nephrotoxic metals.
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Int. J. Environ. Res. Public Health 2014, 11, 2125-2147; doi:10.3390/ijerph110202125
International Journal of
Environmental Research and
Public Health
ISSN 1660-4601
Glyphosate, Hard Water and Nephrotoxic Metals: Are They the
Culprits Behind the Epidemic of Chronic Kidney Disease of
Unknown Etiology in Sri Lanka?
Channa Jayasumana
*, Sarath Gunatilake
and Priyantha Senanayake
Department of Pharmacology, Faculty of Medicine, Rajarata University, Anuradhapura 50008,
Sri Lanka
Health Science Department, California State University, Long Beach, CA 90840, USA;
Hela Suwaya Organization, Malabe 10115, Sri Lanka; E-Mail:
These authors contributed equally to this work.
* Author to whom correspondence should be addressed; E-Mail:;
Tel.:+94-714-393-989; Fax: +94-252-234-464.
Received: 17 December 2013; in revised form: 22 January 2014 / Accepted: 27 January 2014 /
Published: 20 February 2014
Abstract: The current chronic kidney disease epidemic, the major health issue in the rice
paddy farming areas in Sri Lanka has been the subject of many scientific and political
debates over the last decade. Although there is no agreement among scientists about the
etiology of the disease, a majority of them has concluded that this is a toxic nephropathy.
None of the hypotheses put forward so far could explain coherently the totality of clinical,
biochemical, histopathological findings, and the unique geographical distribution of the
disease and its appearance in the mid-1990s. A strong association between the
consumption of hard water and the occurrence of this special kidney disease has been
observed, but the relationship has not been explained consistently. Here, we have
hypothesized the association of using glyphosate, the most widely used herbicide in the
disease endemic area and its unique metal chelating properties. The possible role played by
glyphosate-metal complexes in this epidemic has not been given any serious consideration
by investigators for the last two decades. Furthermore, it may explain similar kidney
disease epidemics observed in Andra Pradesh (India) and Central America.
Although glyphosate alone does not cause an epidemic of chronic kidney disease,
Int. J. Environ. Res. Public Health 2014, 11 2126
it seems to have acquired the ability to destroy the renal tissues of thousands of farmers
when it forms complexes with a localized geo environmental factor (hardness) and
nephrotoxic metals.
Keywords: chronic kidney disease of unknown etiology; glyphosate; hard water;
nephrotoxic metals; arsenic
1. Introduction
1.1. Chronic Kidney Disease of Unknown Etiology (CKDu) in Sri Lanka
Starting in the mid 1990s, a Chronic Kidney Disease of Unknown etiology (CKDu) was discovered
among the rice paddy farmers in the North Central Province (NCP) of Sri Lanka [1]. Over the next two
decades, the disease spread rapidly to the other farming areas. The age-standardized prevalence of the
disease is estimated at 15% [2] affecting a total population of 400,000 patients with an estimated death
toll of around 20,000 [3]. The unique feature of this CKDu is that its etiology does not include
commonly known risk factors for CKD such as diabetes mellitus, hypertension and glomerular
nephritis [4]. In 2009, the Sri Lankan Ministry of Health introduced criteria for case definition of
CKDu [5]. These included:
(1) No past history of, or current treatment for diabetes mellitus or chronic and/or severe
hypertension, snake bites, urological disease of known etiology or glomerulonephritis.
(2) Normal glycosylated hemoglobin levels (HbA1C ˂ 6.5%).
(3) Blood pressure ˂160/100 mmHg untreated or ˂140/90 mmHg on up to two
antihypertensive agents.
The CKDu is a disease that progresses slowly [1]. Patients are asymptomatic during most of the
course of the disease. Histopathological findings have shown tubular interstitial nephritis associated
with mononuclear cell infiltration, glomerular sclerosis and tubular atrophy [6]. The disease is
characterized by tubular proteinurea, usually alpha-1 and beta-2 microglobulinuria, and high urine
Neutrophil Gelatinase-associated lipocalin (NGal) levels (>300 ng/mg creatinine) [7,8]. The observed
geographical and socioeconomic disease patterns led to assumptions that environmental and
occupational factors have an important role to play as the main causative agents [9,10].
Tubulointerstitial disease with negative immunofluorescence for IgG, IgM and complement-3 are more
in favor of a toxic nephropathy [4], but commonly known nephrotoxins such as lead (Pb),
non-steroidal anti-inflammatory drugs, aminoglycosides, aristolochic acid and mycotoxins are highly
unlikely as a single cause of CKDu in Sri Lanka. Many victims of CKDu are not aware of being ill
until the end stage and their only treatment options are peritoneal and hemodialysis and ultimately,
kidney transplantation.
A number of research groups, including the World Health Organization (WHO), have conducted
research studies to determine the etiology of this unique type of CKD. There is some consensus that
this is a multifactorial disease. The main factors include chronic exposure to arsenic (As) [1],
Int. J. Environ. Res. Public Health 2014, 11 2127
cadmium (Cd) [11] and pesticides [2,12]. Consumption of hard water, low water intake and exposure
to high temperatures resulting in significant dehydration, are among the other factors. Whatever hypothesis
that is propounded should be able to answer the questions as to why CKDu is confined to certain
geographical areas of Sri Lanka and why there was no CKDu in Sri Lanka prior to the 1990s.
1.2. CKDu and Ground Water Hardness
Places with high ground water hardness and the geographical distribution of the CKDu in Sri Lanka
are well correlated (Figure 1). Hardness of water is caused mainly due to the presence of the
polyvalent metallic cations calcium (Ca), magnesium (Mg), strontium (Sr) and iron (Fe), together with
carbonate, bicarbonate, sulphate and chloride anions [13]. The degree of hardness is classified as, soft,
moderately hard, hard or very hard when the Ca and Mg content is 060 mg/L, 61120 mg/L,
121180 mg/L and >181 mg/L, respectively [14]. Ground water in the CKDu endemic area is found to
be either hard or very hard and contain Ca, Mg, Fe and Sr ions [15].
Figure 1. Geographical distribution of patients with CKDu and ground water hardness in
Sri Lanka. Ground water hardness data- with the courtesy of Water Resources Board
of Sri Lanka.
A highly statistically significant positive correlation (p < 0.008) has already been revealed between
the occurrence of CKDu in Sri Lanka and hard water consumption. Ninety six percent of the
CKDu patients had consumed hard or very hard water for at least five years, from wells that receive
their supply from shallow regolith aquifers [16]. Apart from that, the authors have made the following
observations related to CKDu and the hardness of the drinking water:
Int. J. Environ. Res. Public Health 2014, 11 2128
(a) The number of villagers who complain that the ground water hardness in CKDu endemic
area has increased steadily over the last two decades.
(b) Certain shallow wells (25 m), which were previously been used for drinking purposes are
now abandoned due to high hardness and bad taste.
(c) There are a few natural springs located in the CKDu endemic area where water is not hard.
People who consume water from these sources have been determined to be free from the
(d) Individuals who drink treated water from large water supply schemes (especially in the two
cities of Anuradhapura and Polonnaruwa), while living in the same endemic areas,
do not have the disease.
(e) In the adjoining farming areas of the Northern Province of Sri Lanka, where the ground
water hardness level is known to also be hard or very hard, there have not been any
significant number of CKDu cases reported.
Many scientists who have been involved in research related to CKDu have neglected the hard water
factor, as there is no scientific evidence linking CKD to the consumption of hard water, or the presence
of high Ca or high Mg levels in drinking water. Nevertheless, due to the strong association between
hard water consumption and CKDu, certain researchers have attempted to link hard water with a
number of other factors related to CKDu. Jayasumana et al. [1] have demonstrated that there is a link
between hardness and arsenic toxicity. They have identified toxic levels of arsenic in urine,
hair and nail samples of CKDu patients as well as in apparently healthy individuals living in the
CKDu endemic region. They proposed that arsenic, derived mainly from tainted agrochemicals
(chemical fertilizers and pesticides), when combined with calcium and/or magnesium in the ground
water can ultimately damage the kidney tissues. Even though there is considerable evidence to suggest
that the agricultural workers in the CKDu endemic areas are exposed to arsenic, the exact source and
mode of entry of arsenic remains controversial. However, the totality of scientific evidence gathered so
far has highlighted the fact that an unknown factor (Compound X) originating from agrochemicals,
when combined with hardness/Ca/Mg can cause significant kidney damage; thus explaining many
current observations including the unique geographical distribution of the disease.
2. Compound X
If we assume that the “Compound X” is derived from the agrochemicals and is easily bound to
Ca/Mg/Sr/Fe to ultimately cause damage to the kidneys, then this hypothesis can explain the
geographical distribution of CKDu as well as the occurrence of the disease only after the 1990s.
Political changes instituted in 1977 in Sri Lanka, have lead to economic policies that allowed the
importation and application of agrochemicals on a large scale, especially for paddy farming.
The low concentration of a cumulative nephrotoxin and its bioaccumulation could have taken
1215 years to cause damage to the kidneys leading up to the level of clinically identifiable CKD.
The increase in prevalence of CKDu and the shifting of age at diagnosis to younger age groups over
the years are highly suggestive of the cumulative nature of the toxin. Furthermore, a comparatively
low amount of agrochemicals has been used in the Northern Province of Sri Lanka, primarily due to a
prohibition imposed by the government in this province. The prohibition was due to the potential of
Int. J. Environ. Res. Public Health 2014, 11 2129
these agrochemicals being used in the production of Improvised Explosive Devices (IEDs).
These IEDs were used abundantly by armed groups of the terrorist movement that plagued the country
until 2009 for causing mass destruction. This is the explanation for the fact that CKDu is still not
prevalent in the farming areas of the Northern Province of Sri Lanka where the ground water hardness
has remained high. Based upon these observations, here we summarizes the expected properties of the
chemical Compound “X” that is hypothesized as the incriminating agent of CKDu.
(a) A compound made of recently (23 decades) introduced chemicals to the CKDu endemic area.
(b) Ability to form stable complexes with hard water.
(c) Ability to capture and retain arsenic and nephrotoxic metals and act as a “carrier”
in delivering these toxins to the kidney.
(d) Possible multiple routes of exposure: ingestion, dermal and respiratory absorption.
(e) Not having a significant first pass effect when complexed with hard water.
(f) Presenting difficulties in identification when using conventional analytical methods.
The present authors have continuously searched for a possibility of Compound X over the time
period of interest and noticed that aminophosphonic acid or aminophosphonate (known by the
common chemical name glyphosate) is the most widely used herbicide in the contemporary world [17]
as well as in Sri Lanka. The amount of glyphosate exceeded the sum of all other pesticides imported
into Sri Lanka in 2012 (Table 1) [18]. The former Stauffer Chemical Company (Westport, CT, USA)
initially obtained a patent for aminophosphonic acid as a chelating agent, wetting agent and
biologically active compound [19]. Glyphosate was initially used as a descaling agent to clean out
calcium and other mineral deposits in pipes and boilers of residential and commercial hot water
systems. Descaling agents are effective metal binders, which grab on to Ca, Mg, etc. ions and make the
metal water soluble and easily removable. Later, the Monsanto Company has acquired the chemical
from Stauffer and obtained a patent for aminophosphonate for its herbicidal properties [20].
Table 1. Leading Pesticides imported to Sri Lanka in 2012.
kg or L Approved for Import
Glyphosate (acid equivalent)
Pretilachlor + Pyribenzoxim
2.1. Glyphosate
Glyphosate or N-(phosphonomethyl)glycine is the aminophosphonic acid analog of the natural
amino acid glycine. It was supposed to be first synthesized by Henri Martin in 1950 [21].
The name glyphosate is derived from the word [Gly]cine [phos]phon[ate]. The Monsanto Company
Int. J. Environ. Res. Public Health 2014, 11 2130
acquired another patent for the phytotoxicant properties of N-(phosphonomethyl) glycine [22].
Glyphosate was quickly adopted by almost all farming communities throughout the World and was
hailed as the magical total weed killer. In fact, glyphosate was acclaimed as the pesticide of the turn of
the millennium and as the most significant chemical in modern agriculture [21]. Glyphosate is a
compound with an amphoteric and zwitterion structure containing a basic secondary amino function in
the middle of the molecule, monobasic-carboxylic and dibasic phosphonic acidic sites at both ends,
hence having three functional groups, phosphonate, amino and carboxylic [23] (Figure 2). A zwitterion
is a neutral molecule with positive and negative electrical charges at different locations within the
same molecule. It is different from simple amphoteric compounds that might only form either a
cationic or anionic species depending on external conditionsa zwitterion simultaneously has both
ionic states within the same molecule [24].
Figure 2. Structure of glyphosate molecule and its functional groups.
Further, glyphosate contains both hydrogen cation donor and acceptor functional groups and has
excellent water solubility 12,000 mg/L [25]. The generally accepted mechanism of action of glyphosate is
that it inhibits the enzyme 5-enolpyruvyl-shikimate-3-phosphate synthase (EPSPS) of the shikimate
pathway in the biosynthesis of tryptophan, phenylalanine and tyrosine (aromatic amino acids) [26].
This pathway is present in plants, fungi and bacteria, but not in animals. Apart from the excellent water
solubility and basipetal translocation ability (capability of transportation in the plant from the leaves
towards the stem) [21] glyphosate is considered as the best herbicide ever discovered as it is readily
degraded to non-toxic degradation products [27]. However, these claims have been debated and
Monsanto Company was fined in a legal case with New York Attorney General’s office in 1996 as it
had inaccurately represented the toxicological data of the glyphosate in its formulated product
Roundup. In this case the Monsanto Company agreed to leave out the description of being
environmentally friendly and biodegradable from its advertisements [28].
The stability of glyphosate in water or soil depends on several factors. It interacts strongly with soil
components by forming stable complexes with metal ions. Adsorption is strongly influenced by cations
Int. J. Environ. Res. Public Health 2014, 11 2131
associated with the soil [29] as it is mainly the phosphonic acid moiety that participates in this process.
Therefore, phosphate, which is a component of most fertilizers, competes with glyphosate in soil
adsorption [30]. The typical half life of the glyphosate was found to be 92 days in water and 47 days in
soil [31,32]. However, the absorption of chelating agents or metals has been shown to decrease the
biodegradability of glyphosate (Figure 3) [23,27,3335]. Radioactive
C-glyphosate studies have
shown that half-life can increase up to 7 years [36] or even up to 22 years [37] in the soil. Glyphosate
is a dianion in moderately buffered soils and water systems when the pH is higher than 6.5. This
suggests that under such conditions glyphosate will form strong complexes with metal ions [35]. The
increased solubility of its alkali metal glyphosate can leach into deep soil layers [38]. Further, it has
been shown that amino methyl phosphonic acid (AMPA) the primary metabolite of glyphosate is more
mobile in the soil than the parent compound [39,40]. Detection of glyphosate in the laboratory is very
difficult due to its ionic character, high polarity, high solubility in water, low volatility, insolubility in
organic solvents and strong complexion behavior [41].
Figure 3. Degradation pathways of glyphosate in normal water and in hard water.
2.2. Glyphosate-metal Complex (GMC)
Glyphosate-hard water/Ca/Mg interaction has been the subject of many scientific studies.
The negative influence of hard water on the herbicidal properties of glyphosate is a well-identified
problem in terms of the efficacy of its weed control [35,4247]. Several measures have also been
identified to overcome the antagonism of spray carrier water hardness of glyphosate [48,49].
These strategies mainly depend on the stability of GMC in different pH values. Usually this GMC is
Int. J. Environ. Res. Public Health 2014, 11 2132
stable in basic media and unstable in acidic media. Smith and Raymond 1987 [50] have studied the
solid state and solution chemistry of calcium glyphosate. They have isolated the polymeric chemical
structure of the compound by using single crystal X-ray diffraction. All the adsorption,
photodegradation and biodegradation processes of glyphosate are modified by the presence of metal
ions [51]. Nuclear magnetic resonance (NMR) studies done by Thelan et al indicate the hard water
cations Ca and Mg interact with both phosphonate and carboxyl functional groups of the glyphosate
molecule [46]. Further, they have shown that over time, the association of the cations with glyphosate
progress to a more structured chelate stable orientation. Glyphosate not only forms stable complexes
with Ca and Mg, but also with many other divalent and trivalent metallic cations (Figure 4).
Caetano et al. [52] assessed the stability of glyphosatemetal complexes and found that the strength
of the stability of divalent cations is in the order, Zn > Cu > Ca > Mg and for trivalent cations,
Co > Fe > Cr > Al, respectively. In the same study, the authors extensively studied the stability of
tetrahedral and octahedral glyphosate-metal complexes as well.
Figure 4. Structures of complexes formed by (a) one molecule (b) two molecules of
glyphosate and metal.
When we go back to the CKDu situation in Sri Lanka and hypothesize that glyphosate is
“Compound X, we can explain almost all of the above-mentioned observations coherently. It provides
rational answers for the geographical distribution of the CKDu and the appearance of the disease in the
mid-1990s. Glyphosate and its primary metabolite AMPA can directly leach into the ground water and
easily chelate to Ca, Mg and Sr copiously present in ground water in the North Central Province and
adjacent rice paddy farming areas in the Sri Lanka. Many farmers use hard water to dissolve
Int. J. Environ. Res. Public Health 2014, 11 2133
glyphosate to prepare the spraying solutions as well. Further it is reported that rice paddy farming soil
in CKDu endemic area is rich with Ca, Mg, Fe, Cr, Nickel (Ni), Co and other metals [53,54].
It can easily combine with glyphosate and form complexes, which later leach into the ground water.
Ferric ions also play a significant role in the process of adsorption of glyphosate and AMPA in soil [55].
Furthermore, within a couple of weeks after the spraying of glyphosate farmers apply triple phosphate
(TSP) to the paddy fields. Recent findings have shown that the TSP available in Sri Lanka is
contaminated with significant amounts of Cd, Cr, Ni and Pb [54]. Divalent cations of these nephrotoxic
metals are capable of forming stable compounds with glyphosate [35]. Furthermore, it was also found
that TSP used in Sri Lanka is a very rich source of arsenic [56].
Other modes of ingestion of glyphosate are dermal and respiratory. Low levels of glyphosate have
frequently been detected in the urine of farm workers shortly after the glyphosate application [57].
Farmers in Sri Lanka spray pesticides manually under hot climatic conditions. Glyphosate preparations
are easily dissolved in sweat and absorbed transdermally [58]. As the majority of farmers do not use any
protective gear, absorption through the respiratory route may also play a significant role. Rice is the
staple diet of farmers. Recent findings have revealed that rice, vegetables and raw tobacco available in
the CKDu endemic areas are contaminated with Cd and As [2]. Chewing of betel with tobacco is a
common practice among farmers in Sri Lanka. The phosphorous atom in the phosphonic group in the
glyphosate/AMPA molecule can possibly be replaced by As [59,60]. Following dermal and respiratory
absorption of glyphosate, it can form complexes with nephrotoxic metals and As derived from rice,
vegetables and tobacco within the circulation. As such, we can identify three potential sources of
glyphosate/AMPA-metal complexes:
(a) [Glyphosate/AMPA + Ca/Mg/Fe/Sr ] complex in drinking water.
(b) [Glyphosate/AMPA + Cd/Cr/Ni/Co/Pb/Vanadium (V) or As] complex in food.
(c) [Glyphosate/AMPA coming from dermal/ respiratory route] + low amount of [metals/As]
from water and foods, here the complex is formed within circulation.
Helfter Enterprises, Inc. now doing business as Advanced Biological Concepts has proposed a
structure for glyphosate matrix [61], while Caetano and coworkers [52] have developed a more
advanced and comprehensive structure for glyphosate metal complexes. The latter group has used
density functional theory (DFT) molecular modeling methods to evaluate structural thermodynamic
and electronic effects that govern the complexion between glyphosate and metals. With the permission
of both groups of authors, we used these structures to propose a glyphosate-metal lattice to explain the
possible role played by glyphosate, hardness, As and other nephrotoxic metals in the pathogenicity of
CKDu in Sri Lanka (Figure 5).
This hypothesis also explains the observation of increased ground water hardness in paddy farming
areas in Sri Lanka. Various divalent and trivalent metal glyphosate compounds accumulate in ground
water over the years and made ground water more hard and distasteful. Natural springs located in the
CKDu endemic area are devoid of high Ca and Mg content, hence these natural springs do not retain
glyphosate. In light of this explanation, it is reasonable to hypothesize that glyphosate-metal complex
plays a major role in the CKDu disease process. It explains why CKDu is not present among people
who drink natural spring water or surface water in the disease endemic area. Also the limited use of
Int. J. Environ. Res. Public Health 2014, 11 2134
herbicide and chemical fertilizers in the northern region over the last few decades may be the reason
for lack of CKDu there despite the consumption of hard water by the inhabitants in this area.
Figure 5. Structure of glyphosate-metal-arsenic lattice.
2.3. The Nephrotoxicity of Glyphosate-metal/As (GMA) Lattice
The next important question to be answered is whether the glyphosate-metal complex is
nephrotoxic or not. Nephrotoxicity of As, Cd and other heavy metals is a known fact [62].
Many studies have been conducted to assess the activity of Ca-glyphosate, Mg-glyphosate behavior in
soil water and in plants [38]. The majority of them have been targeted to overcome the antagonistic
ability of Ca/Mg on glyphosate [63]. Although glyphosate has a history of more than 40 years of usage
as an herbicide and it has been almost 50 years since the identification of hardness-aminophosphonic
acid reaction, none of the available studies has focused on the animal or human health effects of
hardness-glyphosate complex. However, glyphosate alone has been the subject of several animal studies.
Jiraunghoorskul et al. [64] described changes in proximal tubular cells of Nile Tilapia exposed to
glyphosate. Ayoola [65] has shown the development of hematopoietic necrosis and severe
pyknotic nuclei, dilatation of bowman’s space, accumulation hyaline droplets in tubular epithelial cells
in the proximal tubule and degenerated tubules in juvenile African catfish exposed to glyphosate.
Seralini and others [66] have shown in a long term study that glyphosate increased serum creatinine,
blood urea and reduced the weight of kidneys of rats who were fed with glyphosate exposed maize.
Tizhe et al. [67] have provided further confirmation that oral exposure of glyphosate increases blood
urea levels and lead to renal dysfunction in rats. Larsen et al. [68] have described the glutathione
peroxidase dependent reduction of cumenehydroperoxide in kidneys of rats exposed to glyphosate in
drinking water. Kruger et al. [69] has shown a similar nephrotoxic effect in dairy cows exposed to
glyphosate. Although EPSPS and the shikimate pathways are not present in animals, the inhibition of
Int. J. Environ. Res. Public Health 2014, 11 2135
other pathways such as cytochrome p450 and aromatase is the possible explanation of genotoxic [70]
and teratogenic [71] activity of glyphosate and the dose dependent effects of round up on human
embryonic and placental cells [72]. Glyphosate has also been documented to induce apoptosis and
necrosis in human umbilical, embryonic and placental cells [73] and cause endocrine disruptive effects
on human cell lines [74].
2.4. Compound X-elusiveness of Detection by Standard Tests
Persistence of glyphosate in water have previously been reported [75,76]. In a recent study done in
Catalonia, Spanish researchers reported that glyphosate was present above the limits of detection in
41% of the ground water samples obtained from areas where intense agricultural activities had taken
place [77]. Another Spanish study has shown that certain chelating agents when present in ground
water can produce false negative results for glyphosate tests, however, the same phenomenon was not
observed in the case of surface water [78]. These researchers found that acidification of ground water
samples to a level of pH 1 can lead to significant changes in the final readings of the glyphosate tests.
Difficulty in the analysis of glyphosate and AMPA in the presence of multivalent cations was
demonstrated in a study done in France [79]. In this study, investigators have shown that only the free
forms of glyphosate and AMPA are sensitive to analytical methods and exact concentration is
underestimated particularly in ground water. In Europe 0.1 μg/L is administratively set as the upper
tolerable level for all the pesticides, including glyphosate in drinking water [80].
2.5. Lack of a Significant First Pass Effect
Once the glyphosate-metal-As lattice enters the circulation it may bypass the normal liver
detoxification process. Usually divalent metal transporter-1 (DMT-1) mediates absorption of heavy
metals in the small intestine [81]. Thereafter, it is transported to the liver and binds with
metallothioneins (MTs)a protein with high content of cystine [82]. The main function of MTs is to
transfer heavy metals to various metalloproteins, transcription factors, and enzymes [83].
Here, we hypothesize that the liver cannot metabolize the GMA lattice due to its unique configuration.
The structure of cystine closely resembles that of glycine [84]. Glyphosate/AMPA is the
aminophosphonic analog of the natural amino acid glycine [21]. As the heavy metals are already
bound to glyphosate/AMPA the binding sites that would have normally attracted MTs are already
occupied. As such, these GMA complexes pass through the liver without a significant first pass effect.
This assumption also explains the normal liver enzyme levels and minimal ultrasonic changes in the
liver of patients with CKDu. Once GMA lattice reaches the kidney, the glomerular-proximal tubular
area provides a distinctive microenvironment conducive to the breakdown of the lattice. Differences in
the pH and the presence of various metabolic products provide this background. Kidneys excrete
50100 meq/day of non-carbonic acid generated daily. This is achieved by H
ion secretion at different
levels in the nephron. The entire daily acid load cannot be excreted as free H
ions. Secreted H
are excreted by binding to either buffers, such as HPO
and creatinine, or to NH
to form ammonium
ions (NH
). Ammonium is produced from glutamine in the proximal tubule [8587].
ions have been used for many decades by agricultural experts to minimize the binding of
glyphosate to hard water which effectively decreases the availability of the active weedicide [88].
Int. J. Environ. Res. Public Health 2014, 11 2136
Further, in analytical chemistry acidification is used as an effective dissociation method of
glyphosate/AMPA complexes to obtain free forms [78]. Therefore, we have further hypothesized that
this high concentration of the NH
ions that releases the heavy metal from the GMA lattice in the
proximal tubular area.
When lattice is broken down, it releases metals and arsenic. Excessive amount of glyphosate/AMPA
and As may start the damage to the glomeruli while As, Cd, Cr, Ni, Co, Pb, V are reabsorbed up to a
certain extent at the proximal tubules resulting in further tubular damage. Long-term exposure to these
substances causes oxidative stress, nitrosative stress, apoptosis and necrosis [8991] in the glomerular
and proximal tubular cells. Glomerular sclerosis, glomerular collapse and tubular interstitial damage
are the result of these pathological mechanisms (Figure 6). Several animal studies have already
demonstrated the reduction of GFR in chronic toxin (adriamycin) induced nephropathy associated with
the development of both tubulointerstitial nephritis and glomerular sclerosis [92]. Furthermore,
Javaid and coworkers [93] have shown that the reduction of GFR is closely correlated with the extent
to which glomeruli are no longer connected to the normal tubules. They suggest that a local extension
of glomerular injury to destroy the tubular neck is an important cause of loss of renal functions.
If we apply the same model to CKDu this explains the comparatively low level of urinary excretion of
creatinine, As, Cd, Cr, Ni, Co, V and glyphosate by CKDu patients (Cases) when compared to healthy
individuals in the same family or living in the same endemic area (Controls) (unpublished data
produced at the California State University, Long Beach, CA, USA). Presence of high levels of As and
Cd in nail and hair samples of CKDu cases as compared to the controls [1,2] is confirmatory evidence
of the exposure and accumulation of As and Cd in the body as the kidneys become increasingly
incapable of excreting them. Destruction of the tubular necks following long term exposure to GMA
lattice also brings about a sudden decrease of renal functions in the later stages of the CKDu which
result in the death of the patient if dialysis or renal transplantation is not done.
3. CKDu Elsewhere
A CKDu epidemic very similar to that of Sri Lanka has been identified among the paddy farmers in
Andra Pradesha southeastern province of India [94]. These authors reported that ground water is the
only available water source in Uddanam and Chikamurthy, two of the areas with the highest
CKDu prevalence. Analysis of samples of drinking water revealed that metal ions and trace elements
in drinking water were within allowable limits, and thus not expected to lead to any deleterious effects
on human health. However, in these findings it was clearly shown that the total hardness, Ca, Mg and Sr
values are quite high. Especially in Chikamurthy area, some of the drinking water samples exceed
1,000 mg/L of total hardness. The authors may not have paid enough attention to this finding as
hardness is not identified as a nephrotoxin or as causing significant human health problems,
apart from being a suggested risk factor for exacerbation of eczema [13]. This is exactly the same
situation that happened in Sri Lanka. The Sri Lanka Ministry of Health and the WHO conducted a joint
investigation and an evaluation of CKDu in Sri Lanka from 2008 to 2013. In the third progress report
of the WHO handed over to the Ministry of Health Sri Lanka on 19 February 2012, it has been mentioned
that the waters in the 99% of the sources used by patients with CKDu are hard to very hard [95]. However,
this factor has not received any further attention when the WHO and the Ministry of Health produced
Int. J. Environ. Res. Public Health 2014, 11 2137
their final scientific publication [2]. The inability to detect glyphosate-metal complexes using the
commonly used analytical methods may have deterred the investigators in both Sri Lanka and Andra
Pradesh from looking further into the role of these compounds in CKDu.
Figure 6. GMA lattice hypothesis in summary.
An epidemic of tubular nephropathy has been identified among young male farm workers in
sub-regions of the Pacific coasts of the Central American (CA) countries of El Salvador, Nicaragua
and Costa Rica [96,97]. Like the Sri Lankan and Indian scenarios, the etiology is not linked to the most
frequent causes of CKD such as diabetes mellitus and hypertension. Rubio et al. [98] estimated a death
toll of at least 20,000 in the CA region for the last two decades. In El Salvador, hospitalization for
CKD increased by 50 percent from 2005 to 2012 and today, it has become the leading cause of
hospital deaths. A total of 39,000 of hospitalized cases of CKDu in El Salvador were reported,
while 1,474 of them were below the age of 20 years [99]. Clinical, biochemical and histopathological
characteristics of CKDu in both Sri Lanka and CA shares a very similar pattern [100].
Int. J. Environ. Res. Public Health 2014, 11 2138
Therefore, it’s logical to argue that the etiologies in both regions could have many commonalities.
The disease is common in sugarcane cultivating areas in CA where some of them previously used to
grow cotton [101]. Both sugarcane and rice belong to the grass family and need a comparatively higher
amount of agrochemicals in large-scale cultivation [102]. Glyphosate is the leading pesticide used in
El Salvador as well [103]. If we apply the same hypothesis to explain the CKDu in CA it can logically
explain the occurrence of disease among male farm workers in pacific coastal line. The CA Pacific
coastal line belongs to the volcanic belt [104,105]. In this region soil and groundwater naturally
contain high amounts of metals and As [106]. These levels of As could be additive to the As which
originated from fertilizers and agrochemicals as pesticides with inorganic As were commonly used in
cotton cultivation. When sugarcane became the leading crop in the Pacific coastal line
after 1990s [107], this crop could have used huge amounts of glyphosate, 2,4-D and other pesticides.
These conditions make it highly the suitable for the formation of a GMA lattice in ground water and
soil with the consequent bioaccumulation in people living in this area. The El Salvador National
Institute of Health also confirmed that the water from shallow wells had been the main drinking water
source for the majority of CKDu patients in the country. Furthermore, they have detected significant
amounts of hardness, As and heavy metal levels in their water samples [108].
4. Glyphosate as “Compound-X”Available Evidence and Areas for Further Research
To prove that glyphosate is the “Compound-X” that chelates with calcium and the other metals to
become the causative agent of CKDu, one has to establish a clear chain of evidence. The first link in
this chain is a well-established fact as shown earlierthat is, glyphosate is a strong metal chelator
(for Ca, Mg, Sr, Cd, Cr, Ni, Co, Pb); It is immobilized in soil by chelating with soil cations;
It persists and accumulates in soil and plants for extended periods (years)therefore, these immobilized
chelates can contaminate the water table.
The second link in the hypothesis is to confirm that the water from the wells which the
CKDu patients have used is contaminated with glyphosate and metal ions. In another study that is
ongoing at California State University, Long Beach, CA, USA we have tested water samples (n = 50)
from these contaminated wells and found that almost all of them contained glyphosate with high
content of Ca and other metals. The authors had to use a special Enzyme Linked Immuno-Sorbent
Assay (ELISA) test to detect these glyphosate-metal complexes, as they are not amenable to the
conventional analytical methods. Glyphosate and heavy metals were also found in the urine of both
CKDu patients as well as the control subjects who lived in the CKDu endemic area. This is not
surprising as most of the controls drank water from the same wells. Therefore, we have confirmatory
proof on the ingestion of these complexes in drinking water and excretion of components of the
complex in urine. The manner in which the glyphosate metal complexes are absorbed through the
intestines needs further research, perhaps beginning with animal models. None of the CKDu patients
(n = 125) showed any significant elevation of liver enzymes or ultrasound evidence of detectable liver
pathology. This is the best evidence that we have so far about the escape from the first pass
metabolism by the glyphosate metal complexes. This is the same reason why we see more renal
manifestations in As poisoning of CKDu patients. However, we occasionally see the classic cutaneous
and liver manifestations only in some CKDu patients with advanced renal damage [1].
Int. J. Environ. Res. Public Health 2014, 11 2139
Acquavella et al. [57] have demonstrated how the glyphosate excretion increased in 48 farmers and
their families after spraying. However, they have not separately assessed the contributions of the
dermal and respiratory routes of exposure. Further research should be undertaken to study how
glyphosate is absorbed into the circulation through dermal and respiratory routes, particularly after
spraying the pesticide.
The third link in this hypothesis is how the glyphosate metal complex contributes to renal damage.
From current renal physiology it is well known that ammonium ions are generated in proximal tubule.
In fact, this is the principle component of the acid excretion of the kidney [109]. It is also well known
from USA studies that ammonium sulphate is used as a buffer to release glyphosate bound to metal
ions [88]. Therefore, it is plausible to assume that this same mechanism is in effect in the proximal
tubule. However further research including renal biopsies and animal studies are necessary to confirm
that this is actually the same mechanism that is at work within the renal tubules.
5. Conclusions
CKDu, the major health issue in the rice paddy farming areas in Sri Lanka, has been the subject of
many scientific and political debates over the last decade. Although there is no agreement among
scientists about the etiology of the disease, a majority of them have concluded that this is a toxic
nephropathy. None of the hypotheses put forward so far could explain coherently the totality of
clinical, biochemical, histopathological findings, and the unique geographical distribution of the
disease and its appearance since the mid 1990s.
The strong association of the consumption of hard water and occurrence of CKDu has been
subjected to many discussions among investigators, but none of the available theories could explain
this relationship coherently. Here we have explained the association by using glyphosate,
the most widely used herbicide in the disease endemic area. The strong metal chelating property of
glyphosate and related compounds is a well-known fact. However, the human health effects of
glyphosate-metal complexes have not been given any serious consideration by investigators for last
four decades. Huge advertising campaigns by glyphosate as the best ever herbicide discovered by
mankind, reiteration of the easily degradable nature of the original compound in a natural environment
and the difficulties in the laboratory detection may have been the reasons for this delay. Results being
produced through the current study that is ongoing in the California State University, Long Beach are
highly supportive of this hypothesis. Stability of glyphosate metal complexes in various environmental
conditions and nephrotoxic properties of the compound should be the subjects of further investigation.
The GMA lattice hypothesis gives rational and consistent explanations to the many observations
and unanswered questions associated with the mysterious kidney disease in rural Sri Lanka.
Furthermore, it may explain the similar epidemics of CKDu observed in Andra Pradesh, India and
Central America. Although glyphosate alone does not cause an epidemic of chronic kidney disease,
it seems to have acquired the ability to destroy the renal tissues of thousands of farmers when it forms
complexes with a localized geo environmental factor (hardness) and nephrotoxic metals. It is logical to
find out other agricultural areas in the World where excessive use of glyphosate and drinking ground
water with high hardness and the contamination of ground water and food with nephrotoxic metals
have overlapped in causing kidney damage.
Int. J. Environ. Res. Public Health 2014, 11 2140
The authors wish to acknowledge the assistance provided by the Hela Suwaya Organization.
According to the prevailing Buddhist philosophical values within the country, no animal models were
used in the current study. The Ministry of Agriculture, Sri Lanka, sponsored the analytical aspects of
this study for limited testing of the hypothesis.
Author Contributions
All three authors have equally contributed to develop the hypothesis. Channa Jayasumana and
Sarath Gunatilake wrote the manuscript.
Conflicts of Interest
The authors declare no conflict of interest.
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... Glyphosate is a known carcinogen and can also break down the tight junctions in the intestinal epithelium, further increasing gut permeability. Glyphosate also has a patent for being an antibiotic, which can kill off the natural microbiome in our gut, affecting our microbiome diversity and causing a disruption in the population of bifidobacterial [59,60,61]. ...
... Because early detection will help prevent the worsening of CKD and boost survivability, worldwide screening systems are being upgraded. Because of this, accurate epidemic-related knowledge of CKD at the national and international levels is very important in involving key stakeholders, such as patients, general practitioners, nephrologists, and financing organizations, who enable the healthcare system to plan and enforce effective preventive policies [4][5][6]. ...
Full-text available
In the modern world, chronic kidney disease is one of the most severe diseases that negatively affects human life. It is becoming a growing problem in both developed and underdeveloped countries. An accurate and timely diagnosis of chronic kidney disease is vital in preventing and treating kidney failure. The diagnosis of chronic kidney disease through history has been considered unreliable in many respects. To classify healthy people and people with chronic kidney disease, non-invasive methods like machine learning models are reliable and efficient. In our current work, we predict chronic kidney disease using different machine learning models, including logistic, pro-bit, random forest, decision tree, k-nearest neighbor, and support vector machine with four kernel functions (linear, Laplacian, Bessel, and radial basis kernels). The dataset is a record taken as a case-control study containing chronic kidney disease patients from district Buner, Khyber Pakhtunkhwa, Pakistan. To compare the models in terms of classification and accuracy, we calculated different performance measures, including accuracy, Brier score, sensitivity, Youdent, specificity, and F1 score. The Diebold and Mariano test of comparable prediction accuracy was also conducted to determine whether there is a substantial difference in the accuracy measures of different predictive models. As confirmed by the results, the support vector machine with the Laplace kernel function outperforms all other models, while the random forest is competitive.
... And with over 280 million pounds of glyphosate sprayed in the United States annually, chemical weed control in agriculture has become heavily scrutinized due to the extensive use of this herbicide [1]. The usage of glyphosate in agriculture has been linked to many health issues including cancer [2], as well as Parkinson's disease, infertility, and fatal kidney disease [3]. Moreover, long-term problems with herbicides include accumulation in the soil, which can damage vine roots, contaminate surface water through runoff, and leach into groundwater [4]. ...
... Sin embargo, a nivel nacional, aun no se ha establecido ninguna normativa, aunque en la Resolución 2115 de 2007, se menciona que la sumatoria de productos de agroquímicos en el agua potable no debe ser superior a 0.1 ppm. La presencia de glifosato en el agua está relacionada con algunos efectos potenciales en la salud de los seres humanos tales como: diversas formas de cáncer, daño renal y afecciones mentales como el trastorno por déficit de atención e hiperactividad (TDAH), autismo, Alzheimer y la enfermedad de Parkinson, así como problemas reproductivos y renales (Fluegge & Fluegge, 2016;Fortes et al., 2016;Jayasumana et al., 2014;Kwiatkowska et al., 2017;Mesnage et al., 2015;Watts et al., 2016). ...
Conference Paper
El Departamento de Norte de Santander, basa su economía principalmente en el sector agropecuario, para el caso del municipio de Ocaña y circunvecinos, predominan cultivos de cebolla, frijol y tomate, favorecido por su ubicación en una zona de clima templado, sin embargo, para el control de las malezas asociadas a estos cultivos, se utilizan grandes cantidades de herbicidas, los cuales tienen un mayor contacto con los cuerpos de agua debido a que estos cultivos se desarrolla en zonas cercanas a la ronda de rio. Por lo anterior, esta investigación tuvo como fin cuantificar la presencia del glifosato en las fuentes de agua superficial y potable del Rio Algodonal, uno de los ríos con los cuales se abastece el municipio de Ocaña; para ello, se evaluaron dos puntos, uno en el agua superficial cruda; el cual, de acuerdo con el Índice de Calidad del Agua-ICA, se encontraba entre regular y aceptable; el segundo punto en el agua potable que de acuerdo con el Índice de Riesgo de la Calidad del Agua - (IRCA) se determinó que no presentaba ningún riesgo. El herbicida se cuantificó mediante espectrofotometría (ultravioleta-visible), determinando una concentración en el agua potable de 0.316 ppm, sobrepasando los niveles máximos establecidos en la Resolución 2115 del 2007 de 0.1 ppm; por su parte el valor detectado en el agua superficial de 0.887 ppm, no se pudo valorar a la luz de la normativa vigente, porque aun cuando esta contempla la categoría toxicológica, el glifosato no califica dentro de dicha categoría por ser considerado ligeramente tóxico, por lo cual no se establece un rango de medición permisible para este tipo de fuentes. Por su parte, con la concentración hallada en el agua potable se realizó la evaluación cuantitativa de riesgos para la salud humana, determinando que, según las directrices para la calidad del agua potable de Canadá y la Organización Mundial de la Salud, presentaban un riesgo moderado.
Chronic kidney disease of uncertain etiology (CKDu) is a global health concern affecting tropical farming communities. CKDu is not associated with typical risk factors (e.g., diabetes) and strongly correlates with environmental drivers. To gain potential insights into disease etiology and diagnosis, here we report the first urinary proteome comparing CKDu patients and non-CKDu controls from Sri Lanka. We found 944 differentially abundant proteins (DAPs). In silico analyses identified 636 proteins of likely kidney and urogenital origin. As expected, renal tubular injury in CKDu patients was evinced by the increase in albumin, cystatin C and β2-microglobulin. However, several proteins typically elevated under CKD, including osteopontin and α-N-acetylglucosaminidase, were decreased in CKDu patients. Further, urinary excretion of aquaporins found higher in CKD, was lower in CKDu. Comparisons with previous CKD urinary proteome datasets revealed a unique proteome for CKDu. Notably, CKDu urinary proteome was relatively similar to that of patients with mitochondrial diseases. Further, we report a decrease in endocytic receptor proteins responsible for protein reabsorption, megalin and cubilin, that correlated with an increase in abundance of 15 of their cognate ligands. Functional pathway analyses identified kidney specific DAPs in CKDu patients denoted significant changes in the complement cascade and coagulation systems, cell death, lysosomal function and metabolic pathways. Overall, our findings provide potential early detection markers to diagnose and distinguish CKDu and warrant further analyses on the role of lysosomal, mitochondrial, and protein reabsorption processes and their link to the complement system and lipid metabolism in CKDu onset and progression.
Os herbicidas à base de glifosato (HBGs) contém, além do principio ativo (glifosato), outras substâncias como surfactantes e adjuvantes. Este artigo teve como objetivo a apresentação de uma revisão da literatura acerca dos riscos à saúde humana, de animais e aos ecossistemas, associados à exposição aos HBGs. Espera-se que o conteúdo possa ser útil ao aperfeiçoamento das práticas e políticas publicas relacionadas ao uso dos referidos agrotóxicos. Para a realização da presente pesquisa, foram consultadas bases de dados disponíveis em portais de periódicos institucionais. Descreve-se que, embora sejam aplicados sobre plantas, os HBGs são levados para longe do local de aplicação, pelo vento, pela água, pela colheita de pólen, grãos, raízes, folhas e frutos. Por serem sistêmicos na planta, chegam às colmeias de abelhas, ao prato do consumidor,a rios, lagos e oceanos. Em contacto com outros organismos, que não plantas, os HBGs causam efeitosdiversos, tais como morte celular, distúrbios reprodutivos, câncer, malformações, autismo, entre outros.
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Background: The growing worldwide prevalence of chronic kidney disease of unknown etiology (CKDu) has been reported since the 1990’s. Neonicotinoids are systemic insecticides started to use in 1990’s with nicotinic acetylcholine receptor competitive modulator action, which may cause renal dysfunction as well as neurological symptoms. Methods: We conducted a field-based case-control study in the North Central Dry-zone of Sri Lanka where CKDu was prevailing. We collected spot urine samples of 92 residents, including 15 CKD patients, 15 CKD family members, and 62 neighbors in May or in December 2015, and analyzed seven neonicotinoids and a metabolite by LC-ESI/MS/MS, in addition to two biomarkers of renal tubule activity, Cystatin-C and L-FABP. The symptoms they complained of were also investigated by interview. Results: Urine was almost acidic and significant correlation was found in urinary concentration of Cystatin-C and L-FABP (r=0.71, p<0.001). In CKD patients in compare to non-CKD participants, urine Cystatin-C and L-FABP were significantly higher (p=0.0013, p<0.001, respectively) and more symptoms complained, e.g. finger tremor, fever, and abnormal behavior, as well as high urine volume, appetite loss, and reduced body weight. The detection rates of neonicotinoids were highest in N-desmethyl-acetamiprid 92.4 %, following dinotefuran 17.4 %, thiamethoxam 17.4 %, clothianidin 9.8%, thiacloprid 3.3%, imidacloprid 2.2%, nitenpyram and acetamiprid 0%. Dinotefuran and thiacloprid had not registered in 2015 in Sri Lanka. Between the concentration of urine Cystatin-C and N-desmethyl-acetamiprid, weak negative correlation was observed (r=-0.19, p=0.077) Conclusions: In CKD patients in the area, high urine Cystatin-C/L-FABP and more neurological symptoms were observed. Neonicotinoids exposure of people living in CKDu-epidemic area in Sri Lanka was common. Further investigation is needed to elucidate that occupational neonicotinoid exposure is one of the causes of CKDu and some neurological symptoms, e.g. appropriate timing of urine sampling.
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O objetivo geral desse artigo é apresentar o panorama da utilização de agrotóxicos no Paraná, e na mesorregião Sudoeste do estado, discutindo a problemática e as consequências do uso exacerbado destes produtos para o ambiente e para a saúde humana. Para tanto, os procedimentos metodológicos estão ancorados na análise de dados secundários oficiais acerca da comercialização de ingredientes ativos, da população residente, da estrutura fundiária e da especialização produtiva. Os resultados demonstram que apesar de o Paraná ter predomínio de agricultura familiar, a especialização produtiva é um traço marcante. A produção de commodities agrícolas, principalmente de soja, milho e trigo, é extremamente dependente do uso de ingredientes ativos como os herbicidas Glifosato e 2,4-D, associados ao desenvolvimento de diversos agravos à saúde humana e ambiental. Na mesorregião Sudoeste, esta realidade não se mostra diferente, o que sugere que a população está sujeita a uma alta exposição ambiental e ocupacional, de modo que as injustiças ambientais são enraizadas ao passo em que os agrotóxicos são impulsionados pelo complexo oligárquico agroquímico e pelo governo brasileiro. Palavras-chave: Agrotóxicos. Agronegócio. Paraná.
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Hard cover, 492 pages Publisher: InTech This book is divided into two sections namely: synthesis and properties of herbicides and herbicidal control of weeds. Chapters 1 to 11 deal with the study of different synthetic pathways of certain herbicides and the physical and chemical properties of other synthesized herbicides. The other 14 chapters (12-25) discussed the different methods by which each herbicide controls specific weed population. The overall purpose of the book, is to show properties and characterization of herbicides, the physical and chemical properties of selected types of herbicides, and the influence of certain herbicides on soil physical and chemical properties on microflora. In addition, an evaluation of the degree of contamination of either soils and/or crops by herbicides is discussed alongside an investigation into the performance and photochemistry of herbicides and the fate of excess herbicides in soils and field crops.
The effects of diluent volume and calcium concentration on glyphosate [ N -(phosphonomethyl] glycine] phytotoxicity were evaluated by adding 0.0, 0.0025, 0.005, 0.01, 0.02, and 0.04 M CaCl 2 to 1.68 kg/ha glyphosate and applying at 130, 190, 375, and 750 L/ha to tall morningglory [ Ipomoea purpurea (L.) Roth] plants that were 10 to 12 cm tall. Thirty days after treatment, glyphosate phytotoxicity was reduced by calcium at diluent volumes of 375 and 750 L/ha. Addition of a sulfonine red dye to the spray solution showed that at 130 L/ha, runoff from tall morningglory leaves was negligible. At 375 and 750 L/ha different volumes, ½ to ¾ of the spray solution, as measured by dye retention, ran off the leaf surface. At 750 L/ha, the water and dye collected at the leaf margins and the spray pattern on the leaf surface was not uniform.
Effects of seven herbicides and two herbicide formulations on the phytotoxicity of glyphosate {[ N -(phosphonomethyl)glycine]} were studied in the greenhouse. All herbicide formulations tested reduced glyphosate toxicity; the degree of reduction among herbicides varied. Type of formulation did not alter the reducing effects of propazine [2-chloro-4,6-bis(isopropylamino)- s -triazine] or propachlor (2-chloro- N -isopropylacetanilide). Liquid formulations of cyanazine {2-[[4-chloro-6-(ethylamino)- s -triazin-2-yl] amino]-2-methylpropionitrile} and linuron [3-(3,4-dichlorophenyl)-1-methoxy-1-methylurea] caused less reduction than the wettable powder formulations, but the liquid formulation of atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)- s -triazine] caused greater reduction than the wettable powder. Inert ingredients of the herbicide formulations were primarily responsible for reduced glyphosate toxicity.
Hard-water cations, such as Ca ⁺² and Mg ⁺² , present in the spray solution can greatly reduce the efficacy of glyphosate. These cations potentially compete with the isopropylamine in the formulation for association with the glyphosate anion. ¹⁴ C-Glyphosate absorption by sunflower was reduced in the presence of Ca ⁺² . The addition of ammonium sulfate overcame the observed decrease in ¹⁴ C-glyphosate absorption. Nuclear Magnetic Resonance (NMR) was used to study the chemical effects of calcium and calcium plus ammonium sulfate (AMS) on the glyphosate molecule. Data indicate an association of calcium with both the carboxyl and phosphonate groups on the glyphosate molecule. Initially, a random association of the compounds occurred; however, the reaction progressed to yield a more structured, chelate type complex over time. NH 4⁺ from AMS effectively competed with calcium for complexation sites on the glyphosate molecule. Data suggest that the observed calcium antagonism of glyphosate and AMS reversal of the antagonism are chemically based.
Calcium chloride in the spray carrier antagonized the toxicity of diethanolamine 2,4-D and sodium 2,4-D, dimethylamine MCPA, sodium bentazon, dimethylamine dicamba and sodium dicamba, sodium acifluorfen, imazamethabenz, ammonium imazethapyr, and isopropylamine glyphosate to kochia in greenhouse experiments. Diammonium sulfate overcame calcium chloride antagonism of the above herbicides, except for glyphosate and imazethapyr. Diammonium sulfate or ammonium nitrate adjuvants overcame calcium chloride and sodium bicarbonate antagonism of dicamba toxicity to kochia and enhanced toxicity of sodium dicamba to nearly equal that of dimethylamine dicamba.
Glyphosate toxicity to wheat was antagonized more by calcium chloride than sodium bicarbonate. Mixtures of the salts at greater than 100 mg L ⁻¹ sodium bicarbonate and 200 mg L ⁻¹ calcium chloride were additive in antagonism of glyphosate in the greenhouse experiments. Surfactant and oil adjuvants did not overcome sodium bicarbonate or calcium chloride antagonism of glyphosate. Oil adjuvants were generally antagonistic to glyphosate. An equation is presented that determines the amount of diammonium sulfate required to overcome glyphosate antagonism based upon the sodium, potassium, calcium, and magnesium cations in the spray carrier.
Glyphosate is often applied with diammonium sulfate to increase weed control. However, many other salts in the spray carrier have antagonized glyphosate phytotoxicity. Research was conducted with wheat as a bioassay species to further determine the influence of various salts on glyphosate phytotoxicity. Cation antagonism of glyphosate occurred with iron > zinc > calcium ≥ magnesium > sodium > potassium. Ammonium cation with hydroxide or most other anions was not antagonistic. Anions of ammonium compounds were of primary importance in overcoming glyphosate antagonistic salts, while the ammonium cation was neutral or slightly stimulatory with certain anions. Sulfate, phosphate, citrate, and acetate anions were not antagonistic, but nitrate and chloride anions were slightly antagonistic when applied as ammonium salts or acids. Antagonism of glyphosate action by sodium bicarbonate and calcium chloride was overcome by phosphoric, sulfuric, and citric acid and phosphate, sulfate, and citrate ammonium salts. Acid and ammonium salts of nitrate and chloride were more effective in overcoming sodium bicarbonate than calcium chloride antagonists of glyphosate. Ferric sulfate antagonism was overcome only by citric, partly by phosphoric and sulfuric but not by nitric and hydrochloric acids or their ammonium salts. Acetic acid, ammonium acetate, and ammonium hydroxide did not overcome any salt antagonism of glyphosate. Glyphosate response to salts was independent of spray carrier pH.