Organochlorine Pesticides in Ethiopian Waters: Implications for Environmental and Human Health

Abstract

Despite the global ban on organochlorine pesticides (OCPs) since the 1970s, their use continues in many developing countries, including Ethiopia, primarily due to the lack of viable alternatives and weak regulations. Nonetheless, the extent of contamination and the resulting environmental and health consequences in these countries remain inadequately understood. To address these knowledge gaps, we conducted a comprehensive analysis of reported concentrations (n=398) of OCPs (n=30) in distinct yet interconnected water matrices: water, sediment, and biota in Ethiopia. Our analysis revealed a notable geographical bias, with higher concentrations found in sediments (0.074 - 1161.2 µg/kg), followed by biota (0.024 - 1003 µg/kg) and water (0.001 - 1.85 µg/L). Moreover, DDTs, endosulfan, and hexachlorohexenes (HCHs) were among the most frequently detected OCPs in higher concentrations in Ethiopian waters. The DDT metabolite p,p'-DDE was commonly observed across all three matrices, with concentrations in water birds reaching levels up to 57 and 143,286 times higher than those found in sediment and water, respectively. The findings showed a substantial potential for DDTs and endosulfan to accumulate and biomagnify in Ethiopian waters. Furthermore, it was revealed that the consumption of fish contaminated with DDTs posed both non-carcinogenic and carcinogenic risks while drinking water did not pose significant risks in this regard. Importantly, the issue of OCPs in Ethiopia assumes even greater significance as their concentrations were found to be eight times higher than those of currently used pesticides (CUPs) in Ethiopian waters. Consequently, given the ongoing concerns about OCPs in Ethiopia, there is a need for ongoing monitoring, implementation of sustainable mitigation measures, and strengthening of OCP management systems in the country, as well as in other developing countries with similar settings and practices.

Full text

Toxicology Reports 12 (2024) 622–630
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Organochlorine pesticides in Ethiopian waters: Implications for
environmental and human health
Elsai Mati Asefa
a
,
*
, Mekuria Teshome Mergia
b
, Yohannes Tefera Damtew
a
,
c
,
Dechasa Adare Mengistu
a
, Faye Fekede Dugusa
d
, Roba Argaw Tessema
a
, Jerry Enoe
e
,
J´
ozef Ober
f
, Berhan M. Teklu
g
, Ermias Deribe Woldemariam
h
a
School of Environmental Health, College of Health and Medical Sciences, Haramaya University, Harar 235, Ethiopia
b
Department of Biology, College of Computational and Natural Science, Hawassa University, Hawassa 05, Ethiopia
c
School of Public Health, The University of Adelaide, Adelaide, South Australia 5005, Australia
d
School of Pharmacy, College of Health and Medical Sciences, Haramaya University, Harar 235, Ethiopia
e
Department of Geomatics Engineering and Land Management, The University of the West Indies, St. Augustine, Trinidad and Tobago
f
Department of Applied Social Sciences, Faculty of Organization and Management, Silesian University of Technology, Roosevelta 26-28, Zabrze 41-800, Poland
g
Plant Quarantine and Regulatory Lead Executive, Ethiopian Agricultural Authority, Addis Ababa 313003, Ethiopia
h
Department of Environmental Management, Faculty of Urban Development Studies, Kotebe University of Education, Addis Ababa 31248, Ethiopia
ARTICLE INFO
Handling Editor: Prof. L.H. Lash
Keywords:
Bioaccumulation factor
DDT
Developing countries
Health risk
Legacy pesticide
Meta-analysis
ABSTRACT
Despite the global ban on organochlorine pesticides (OCPs) since the 1970s, their use continues in many
developing countries, including Ethiopia, primarily due to the lack of viable alternatives and weak regulations.
Nonetheless, the extent of contamination and the resulting environmental and health consequences in these
countries remain inadequately understood. To address these knowledge gaps, we conducted a comprehensive
analysis of reported concentrations (n=398) of OCPs (n=30) in distinct yet interconnected water matrices: water,
sediment, and biota in Ethiopia. Our analysis revealed a notable geographical bias, with higher concentrations
found in sediments (0.074–1161.2 µg/kg), followed by biota (0.024–1003 µg/kg) and water (0.001–1.85 µg/L).
Moreover, DDTs, endosulfan, and hexachlorohexenes (HCHs) were among the most frequently detected OCPs in
higher concentrations in Ethiopian waters. The DDT metabolite p,p
′
-DDE was commonly observed across all three
matrices, with concentrations in water birds reaching levels up to 57 and 143,286 times higher than those found
in sediment and water, respectively. The ndings showed a substantial potential for DDTs and endosulfan to
accumulate and biomagnify in Ethiopian waters. Furthermore, it was revealed that the consumption of sh
contaminated with DDTs posed both non-carcinogenic and carcinogenic risks while drinking water did not pose
signicant risks in this regard. Importantly, the issue of OCPs in Ethiopia assumes even greater signicance as
their concentrations were found to be eight times higher than those of currently used pesticides (CUPs) in
Ethiopian waters. Consequently, given the ongoing concerns about OCPs in Ethiopia, there is a need for ongoing
monitoring, implementation of sustainable mitigation measures, and strengthening of OCP management systems
in the country, as well as in other developing countries with similar settings and practices.
1. Introduction
Organochlorine pesticides (OCPs) are a group of synthetic chemicals
that were widely used in the past to control pests in agriculture and
combating disease vectors in public health. Representative OCP com-
pounds include dichlorodiphenyltrichloroethane (DDT), hexa-
chlorohexene (HCH), lindane, endosulfan, dieldrin, methoxychlor,
chlordane, toxaphene, and dicofol. These compounds vary in their
chemical structure and mechanisms of action [20,28,29]. In general,
OCPs are highly toxic, resistant to degradation, capable of long-range
transport, and prone to bioaccumulation and biomagnication in the
environment, making them persistent organic pollutants (POPs) of
concern [29,5,53,54]. Consequently, they have become ubiquitous in
the environment, being found even in remote locations like polar envi-
ronments and the deep sea [57,72,86].
OCPs enter water resources through various routes, primarily
* Corresponding author.
E-mail addresses: elsyyymati@gmail.com, Elsai.mati@haramaya.edu.et (E.M. Asefa).
Contents lists available at ScienceDirect
Toxicology Reports
journal homepage: www.elsevier.com/locate/toxrep
https://doi.org/10.1016/j.toxrep.2024.06.001
Received 4 April 2024; Received in revised form 28 May 2024; Accepted 6 June 2024

Toxicology Reports 12 (2024) 622–630
623
including surface runoff, erosion, atmospheric drift, and deposition [3,
60]. Once in water bodies, OCPs can sorb to suspended and particulate
organic matter, transfer to sediments, or enter the aquatic food chain.
This can lead to bioaccumulation and, over time, biomagnication in
top predators, including water birds and humans [10,29,9]. Addition-
ally, OCPs can cause mortality, reproductive failure, eggshell thinning,
and immune system suppression among aquatic organisms [40,65,70].
Moreover, epidemiological evidence suggests that human exposure to
OCPs results in various health issues, including reproductive dysfunc-
tion, endocrine disruption, immune system dysfunction, and cancer [33,
35,39,58,85].
Due to their signicant impact on the environment and human
health, countries have implemented bans on the production and use of
OCPs since the 1970s (e.g., the Stockholm Proclamation adopted in
2001). As a result, there has been a substantial decrease in their market
share as they have been replaced by supposedly less toxic alternatives
such as organophosphates and pyrethroids [31,63]. However, despite
the bans, the use of OCPs has persisted in developing countries, pri-
marily driven by their high efciency-to-cost ratio and the lack of
affordable alternatives [31,54,71,8]. Although these pesticides are
purportedly used for vector-borne disease control in these countries,
reports on their illegal use in agricultural activities also exist [4,47,73].
Importantly, the use of OCPs in these countries does not appear to be
ceasing soon due to the increasing incidence of vector-borne diseases,
pest resistance, and weak regulatory policies to control their usage [11,
31]. Therefore, OCPs continue to be a concern in developing countries,
including Ethiopia.
In this regard, studies have indicated a lack of scientic knowledge
concerning the actual eld concentrations of OCPs and their effects on
non-target organisms in developing countries [11,22,36]. Most of the
available evidence is derived from studies conducted in temperate re-
gions, and the limited studies carried out in developing countries have
primarily focused on identifying research hotspots and reporting OCP
concentrations without conducting detailed analyses (e.g., [21,54]). To
address these gaps, we conducted an analysis of OCP contamination in
water resources in Ethiopia, a tropical country. We systematically
collected and analyzed OCP concentrations in Ethiopian water, sedi-
ment, and biota, including sh and water birds. Additionally, we
calculated the bioaccumulation factor (BAF) and biota-sediment accu-
mulation factor (BSAF) and assessed the human health risks associated
with OCP exposure. As such, the outputs of this study will contribute to
lling the existing knowledge gap and can be used to inform policy
decisions and develop mitigation measures towards OCP concerns in
Ethiopia and in other developing countries with similar settings and
practices.
2. Materials and method
2.1. Data collection and processing
To identify relevant studies on organochlorine pesticides (OCPs) in
Ethiopian waters, we conducted a comprehensive systematic search in
the PubMed and Scopus databases. The search terms used were
“Organochlorine pesticides, OCPs, Chlorinated hydrocarbons, Persistent
organic pollutants, chlorinated pesticides,” combined with “Surface
water, Sediment, Biota.” Additionally, we utilized the Publish or Perish
software (https://harzing.com/resources/publish-or-perish) to search
Google Scholar and obtain the top 1000 results. Reference scanning was
also employed to identify additional relevant studies. The search was
limited to Ethiopia without any restrictions on the year of study (see
Asefa et al. [6] for details). In total, 980 studies were retrieved and
screened based on title, abstract, and full texts for inclusion in this study.
Studies were included if they reported concentrations of any OCP
compounds or metabolites in Ethiopian water resources. Studies
focusing on pesticides other than OCPs, developed and validated
analytical methods for OCP monitoring, or non-original review articles
were excluded. Finally, 24 peer-reviewed studies were included to
derive the dataset of OCP concentrations used for analysis in this study
(Supplementary Material (SM) Table S1).
From the included studies, we extracted information on the reported
OCP compounds or metabolites and their concentrations separately for
the water phase, sediments, and biota, whenever available. Addition-
ally, supplementary data such as sampling location, water body type,
sampling year, and limit of detection/quantication (LOD/LOQ) were
also incorporated, if provided. To ensure the quality of the OCP con-
centrations used in our analysis, we critically assessed the methodo-
logical rigor, appropriateness of sampling methods, sample handling
procedures, reliability of analytical tools, and adherence to good labo-
ratory practices for each of the included studies (Table S1; also see Asefa
et al. [6] for details). Importantly, we only included OCP concentrations
that were detected and quantied. In cases where OCPs were detected
but not quantied (n=6), we cautiously included them by converting
them to half of the LOD when applicable [18,75]. The studies reporting
OCP concentrations in Ethiopian water resources were mapped using
QGIS (https://qgis.org/en/site/), utilizing the sample locations and
related information provided in the included studies.
2.2. Meta-analysis
We conducted an analysis of three separate yet interrelated water
matrices: the water phase, sediment phase, and biota (sh and water
birds). The analysis encompassed 30 OCP compounds and metabolites,
with approximately 398 reported concentrations within these matrices
in Ethiopian waters. For each matrix, summary statistics including the
frequency of occurrence, mean, maximum, and 90th percentile con-
centrations of the OCPs were calculated. The pollution source ascer-
tainment for the commonly detected DDTs and HCHs was calculated
using parent/metabolite ratios. For DDTs, the ratio of p,p
′
-DDT/(p,p
′
-
DDE +p,p
′
-DDD) was used, while for HCHs, the ratio of β/
α
+γ-HCH
was utilized. A ratio greater than 1 suggests recent use, while a value
lower than 1 indicates historical usage [26,67]. Furthermore, the
α
/γ-HCH ratio was used to differentiate whether the sources of HCH
metabolites are from lindane or technical HCHs. A ratio greater than 1
indicates the use of a technical mixture of HCHs, while a value lower
than 1 corresponds to the recent utilization of lindane [67].
2.3. Bioaccumulation and biomagnication of OCPs in Ethiopian water
To evaluate the accumulation of OCPs and determine the relative
contribution of water and sediments as contamination sources in Ethi-
opian waters, we calculated the bioaccumulation factor (BAF) and the
biota sediment accumulation factor (BSAF). BAF is a measure used to
quantify the extent to which a chemical substance accumulates in living
organisms relative to its concentration in the surrounding water (Eq. 1).
On the other hand, BSAF, is the ratio of a chemical substance in living
organisms compared to its concentration in the sediment (Eq. 2). Thus,
higher BAF and BSAF values indicate a greater potential for bio-
accumulation ([34,74,82]).
BAF =Cf
Cw
(1)
where BAF is bioaccumulation factor (L/kg), C
f
=OCPs concentration in
sh (µg/kg) and C
w
=OCPs water concentration (µg/L)
BSAF =Cf
Cs
(2)
where BSAF is biota-sediment accumulation factor (µg/kg), C
f
=OCPs
concentration in sh (µg/kg) and C
s
=OCPs sediment concentration
(µg/kg).
E.M. Asefa et al.

Toxicology Reports 12 (2024) 622–630
624
2.4. Health Risk assessment
To assess the health risks associated with OCPs among the general
population (adults weighing 70 kg) in Ethiopia, non-carcinogenic and
carcinogenic risks were evaluated. The assessment focused on dietary
exposure to DDTs through drinking water and sh consumption, using
risk assessment models provided by the United States Environmental
Protection Agency [78]. DDT was chosen for evaluation due to its high
frequency of detection and its potential for biomagnication in Ethio-
pian waters. The chronic daily intake (CDI) of DDT (in mg/kg/day) was
determined by considering the mean and maximum concentrations, as
shown in Eq. 3.
CDI =Cwater or fish ×IngR ×EF ×ED
BW ×AT (3)
where C
water or sh
is the concentration of DDTs in water (µg/L) or sh
(µg/kg); IngR is ingestion rate (2 L/day for water or 0.027 kg/day for
sh; EF is exposure frequency (365 days/year); ED is exposure duration
for carcinogenic risk (70 years) and non-carcinogenic risk (30 years);
BW is average of body weight (70 kg); AT is average time for carcino-
genic risk (70 years ×365 days/year) and non-carcinogenic risk (30
years ×365 days/year).
Non-carcinogenic health risks were assessed using the hazard index
(HI), which is obtained by dividing the CDI by the reference dose (RfD)
(Eq. 4). Carcinogenic health risks, or cancer risks (CR), were evaluated
by multiplying the CDI by the cancer slope factor (CSF) (Eq. 5).
HI =CDI
RfD (4)
where CDI is the chronic daily intake of DDTs; RfD (µg/kg/day) is the
maximum allowable dose per day of the DDTs causing non-carcinogenic
health effect.
CR =CDI ×CSF (5)
where CDI is the chronic daily intake of DDTs (µg/kg/day), and CSF (µg/
kg/day) is the cancer slope factor for DDTs.
The RfD for DDT (0.5 µg/kg/day) and CSF (350 µg/kg/day) were
obtained from the USEPA’s integrated risk information system [79]. In
addition, hypothetical values for water consumption of 2 L/day and sh
consumption of 0.027 kg/day for Ethiopians were utilized, as per US
EPA [76] and FAO [19], respectively. Acceptable values for
non-carcinogenic and carcinogenic health risks were considered to be HI
less than 1 and CR within the range of 10
−6
to 10
−4
, respectively [78].
All statistical computations and graphical illustrations were carried out
utilizing the open-source software package R (version 4.3.0: https://cr
an.r-project.org).
3. Results and discussion
3.1. OCPs in Ethiopian water
The studies included in our analysis yielded a comprehensive dataset
comprising approximately 398 concentrations for 30 OCP compounds
and their metabolites across different matrices, including water
(n=115), sediment (n=88), and biota (n=195). Notably, among the 24
studies included, 17 focused specically on the Rift Valley (RV) region of
Ethiopia, accounting for about 82 % of the total dataset (Fig. 1 and
Table S1). Similar studies conducted in Ethiopia and elsewhere also
reported such a geographical bias [50,56,6,66]. The concentration of
studies in the RV region can be attributed to several factors. Firstly, the
region has a long history of extensive OCP use, which has likely resulted
in higher levels of contamination and environmental impact. Secondly,
the illegal utilization of these pesticides is prevalent in the area [4,44,
45]. Additionally, the region is proximate to research institutions and
advanced laboratories, contributing to the increased research interest in
the area.
The detection of OCPs across the three matrices analyzed varied.
Most detections were reported in sediments (n=26) and biota (n=23),
with water (n=15) having the lowest number of detections (Table S2).
The overall OCP concentrations in water resources in Ethiopia ranged
from 0.001 to 1161.2 µg/L, with a mean concentration of 33.77 µg/L
(Fig. 2). The higher concentrations were reported in sediments (90th
percentile =153.015 µg/kg), followed by biota (90th percentile =
55.2 µg/kg) and water (90th percentile =0.89 µg/L) (Table S2).
Furthermore, the detection of OCPs among the subcategories within
Fig. 1. Spatial distribution of OCP studies in Ethiopian water resources.
E.M. Asefa et al.

Toxicology Reports 12 (2024) 622–630
625
each matrix also varied. Water in reservoirs was found to be less polluted
by OCPs compared to rivers and lakes, while the sediment in lakes was
less polluted compared to rivers and reservoirs. However, in both cases,
it was found that river water resources are highly exposed to OCPs,
indicating that they are more vulnerable ecosystems in Ethiopia (Fig. 3).
Studies also reported that rivers are more exposed to pesticides,
although the extent depends on factors such as surrounding land use and
water ow patterns [27,37,80]. Moreover, the biota subcategory
included a total of seven sh species and four bird species, of which sh
had the highest number of reported OCPs (about 66 %) compared to
birds. However, high OCP concentrations were reported in birds (Fig. 4).
In this regard, signicant variations among the species analyzed were
also observed, in agreement with other studies [23,24,56].
Among the OCPs analyzed, DDTs, endosulfan, and HCHs were the
most frequently detected in Ethiopian waters, with p,p
′
-DDE (n=70)
being the most commonly found compound across all three matrices
examined (Fig. 2). The overall highest reported concentrations of OCPs
were 1161.2 µg/kg in sediments and 1003 µg/kg in birds, corresponding
to lindane and the DDT metabolite p,p
′
-DDE, respectively (Figs. 3 and 4).
Similar studies conducted elsewhere also showed a similar pattern
[54–56,61,62,67].
The mean concentrations of DDTs ranged from 0.002 to 1003 µg/L,
with an average concentration of 34.588 µg/L and high detections in
birds and sh (Fig. 4). Source ascertainment indicated that DDTs in
Ethiopian waters were less dominated by the parental metabolites,
indicating historical inputs in contrast to the results of the study con-
ducted in India [62]. The overall occurrence of DDT metabolites in
Ethiopian waters followed the order of p,p
′
-DDE >p,p
′
-DDD >p,p
′
-DDT
>o,p
′
-DDT >o,p
′
-DDE >o,p
′
-DDD (Table S2). The higher detection of p,
p
′
-DDE in this study could be attributed to the biological persistence of
this metabolite compared to other DDT compounds [24,30,84].
Endosulfan, another frequently detected OCP, exhibited an overall
concentration ranging from 0.023 to 341.5 µg/L, with a mean concen-
tration of 13.297 µg/L (Figs. 3 and 4). The mean concentrations of
endosulfan were in the order of
α
-endosulfan >β-endosulfan >endo-
sulfan sulfate (Table S2). The concentrations of HCHs ranged from 0.029
to 5.68 µg/L, with an average concentration of 0.686 µg/L and high
detections in sediments and sh (Figs. 3 and 4). No HCHs were reported
in water samples. The order of HCH isomers was HCH-β >HCH-
α
>
HCH-γ >HCH-δ (Table S2). Source ascertainment indicated recent
usage of HCHs in the surrounding areas, probably from the use of
lindane. Similar results have also been reported in other studies [61,62,
67,81].
Overall, the ndings indicate higher concentrations of OCPs across
different matrices in Ethiopian waters. However, there is signicant
variation in the distribution and concentrations of OCPs in these
matrices and their subcategories. This can likely be attributed to several
factors, including the physicochemical properties of the compounds,
their persistence in the environment, and the specic characteristics of
the matrices [10,20,28,29,57,9]. The concentration of p,p
′
-DDE in birds
was found to be up to 57 and 143,286 times higher than the concen-
trations in sediment and water, respectively, clearly demonstrating the
biomagnication of DDTs in the food chain of the Ethiopian aquatic
ecosystem. Importantly, when comparing the levels of OCPs with
currently used pesticides (CUPs) in Ethiopia, as presented in Asefa et al.
[6], the levels of OCPs reported in this study were found to be eight
times higher. This demonstrates the continued presence and concern of
OCPs in Ethiopia and their signicance compared to CUPs. Similar
conclusions have also been drawn in studies conducted in other tropical
environments [11,12,32,52–55,64,83].
3.2. BAF and BSAF of OCPs in Ethiopian water
The highest bioaccumulation factor (BAF) values were observed for
p,p
′
-DDE, endosulfan-
α
, p,p
′
-DDT, and p,p
′
-DDD, indicating their signi-
cant tendency to bioaccumulate in biota compared to their concentra-
tion in water (Table S2). Conversely, some OCPs, such as lindane,
heptachlor, and chlordane-
α
, showed lower BAF values, indicating
relatively lower bioaccumulation potential. Regarding the bio-
accumulation from sediments, the highest values of the BSAF were
observed for endosulfan-
α
, endosulfan-β, and chlordane, indicating their
signicant ability to accumulate in sh originating from sediments
(Table S2). In contrast, lower BSAF values were observed for DDT me-
tabolites, suggesting that the main source of sh contamination is
through bioconcentration and bioaccumulation directly from the sur-
rounding water, rather than from sediments. In line with these ndings,
Fig. 2. OCP concentrations among the three water matrices in Ethiopia, water (n=115), sediment (n=88), and biota (n=195).
E.M. Asefa et al.

Toxicology Reports 12 (2024) 622–630
626
eld studies conducted in Ethiopia have shown that OCPs, especially
DDT metabolites, biomagnied across aquatic food webs with
increasing trophic levels [15,46,7,87].
However, it is important to interpret these results with caution, as
our study found higher concentrations of DDTs in biota, particularly in
sh consuming birds, indicating the biomagnication of DDTs in Ethi-
opian waters (see Section 3.1). Therefore, the bioaccumulation of OCPs
in sh in Ethiopia may not be solely attributed to direct uptake from the
surrounding environment but also to uptake through the food chain and
food web, which play an important role in the Ethiopian aquatic
ecosystem. While some studies have suggested that direct uptake of
compounds from water does not signicantly contribute to the total
contaminant concentration in organisms [34,82], our study found the
opposite result, with bioaccumulation of OCPs better represented by
BAF (mean: 264) than BSAF (mean: 48.3). This difference could be
attributed to various factors, including the characteristics of tropical
waters, sh behavior, sediment characteristics, and properties of OCPs
[59]. However, to gain a better understanding of the fate of these
pesticide compounds in Ethiopian waters, differences in trophic levels,
annual exposure and absorption, and annual net retention among
different sh species should be considered.
3.3. Human health risks assessment
We found that the general population in Ethiopia is exposed to
higher health risks associated with dietary intake of DDTs through sh
consumption rather than through drinking water. The overall non-
carcinogenic risks in the water were within acceptable limits for
drinking, with mean concentrations ranging from 9.34E-03–3.59E-01
and maximum concentrations ranging from 4.00E-02–2.86E-02
(Table 1). In addition, no cancer risks associated with DDT exposure
through drinking water in Ethiopia were observed. However, it is
important to note that if the drinking water source is a river, the risks
may be higher, especially with long-term exposure or higher consump-
tion rates due to its higher DDT concentrations, which could lead to
health effects.
On the other hand, the risks associated with DDT exposure through
sh consumption were found to be unacceptable. The overall non-
carcinogenic risks ranged from 3.59E-01–3.20E+00, and the cancer
risks ranged from 5.13E-04–4.57E-03 (Table 1). Specically, consuming
Fig. 3. OCP concentrations in A (water; n=115) and B (sediments; n=88) and their subcategories in water resources in Ethiopia.
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Toxicology Reports 12 (2024) 622–630
627
Barbus intermedius, Clarias gariepinus, and Oreochromis niloticus posed
both non-carcinogenic and cancer risks, while Carassius auratus posed
cancer risks among the general population in Ethiopia (Table 1). It is
important to note that these sh species are commercially important in
Ethiopia and commonly consumed across the country [2], although the
consumption rate varies [16,69]. Therefore, individuals who consume
sh more frequently and prefer to consume various species will have a
higher intake of DDTs, thus increasing the associated risks.
DDT and its metabolites may act as endocrine disruptors and have
carcinogenic properties. They are associated with adverse health out-
comes such as breast cancer, diabetes, abortion, and cognitive impair-
ment [17,68]. In line with the ndings of our study, biomonitoring
studies conducted in Ethiopia have also reported higher concentrations
of DDT metabolites, i.e., p,p
′
-DDT and p,p
′
-DDE, in human serum [1,41].
Furthermore, the epidemiological study by Mekonen et al. [42] sug-
gested that OCPs are risk factors for breast cancer. The study found that
a one-unit increase in p,p
′
-DDT concentration doubled the odds of
developing breast cancer (AOR: 2.03, 95 % CI: 1.041–3.969) [42]. In
this regard, although the majority of studies in Ethiopia have focused on
the occupational aspects of pesticide exposure, associated adverse ef-
fects such as respiratory health problems and neurobehavioral symp-
toms have also been reported in the country [43,48,49]. However,
further research is needed to comprehensively investigate OCP exposure
and adverse effects through all direct and indirect pathways, focusing on
environmental exposures. Moreover, strict OCP regulations are urgently
required to protect human health in Ethiopia.
3.4. Result implications and conclusion
This study presents the rst comprehensive analysis of organochlo-
rine pesticides (OCPs) in aquatic ecosystems in Ethiopia. The study ex-
amines various aspects, including bioaccumulation, biomagnication,
and potential health risks associated with dietary exposure to OCPs. The
need for this study arises from several knowledge gaps that exist in
developing countries regarding the impact of legacy pesticides. Despite
the prohibition of OCPs in many countries, their use continues in
developing countries including Ethiopia, posing a signicant threat to
biodiversity [31,54,71,8]. However, there is limited evidence regarding
the extent of contamination and the resulting consequences for human
and environmental health risks in Ethiopia. To address these gaps, we
conducted a comprehensive analysis of three interrelated water matrices
(water phase, sediment phase, and biota) in Ethiopia, using 30 OCP
compounds and metabolites, totaling approximately 398
concentrations.
Our ndings revealed high concentrations of OCPs in Ethiopian
waters. However, there is signicant variation among the matrices and
their subcategories analyzed. Importantly, about 82 % of the OCP con-
centrations included in this study were in the Rift Valley (RV) region of
Fig. 4. OCP concentrations in C (biota; n=195) and its subcategories in water resources in Ethiopia.
Table 1
Non-carcinogenic and carcinogenic health risks associated with dietary intake of DDTs through drinking water and sh consumption among the general Ethiopian
population. Risks were calculated for the mean and maximum concentrations reported, and values exceeding safe levels are indicated in bold font.
Dietary consumption Concentration Mean ADI Non-Carcinogenic Carcinogenic Concentration Maximum ADI Non-Carcinogenic Carcinogenic
Drinking Water 0.14 0.00 7.93E-03 1.13E-05 0.70 0.02 4.00E-02 5.71E-05
Lake 0.21 0.01 1.18E-02 1.69E-05 0.50 0.01 2.86E-02 4.08E-05
Reservoir 0.05 0.00 2.76E-03 3.94E-06 0.67 0.02 3.83E-02 5.47E-05
River 0.16 0.00 9.34E-03 1.33E-05 0.70 0.02 4.00E-02 5.71E-05
Fish 6.29 0.18 3.59E-01 5.13E-04 56.00 1.60 3.20Eþ00 4.57E-03
Barbus intermedius 22.61 0.65 1.29Eþ00 1.85E-03 56.00 1.60 3.20Eþ00 4.57E-03
Carassius auratus 4.91 0.14 2.80E-01 4.01E-04 12.49 0.36 7.14E-01 1.02E-03
Clarias gariepinus 8.13 0.23 4.64E-01 6.63E-04 33.69 0.96 1.93Eþ00 2.75E-03
Cyprinus carpio 6.04 0.17 3.45E-01 4.93E-04 - - - -
Oreochromis niloticus 4.28 0.12 2.44E-01 3.49E-04 19.16 0.55 1.09Eþ00 1.56E-03
Tilapia zilli 1.77 0.05 1.01E-01 1.45E-04 4.71 0.13 2.69E-01 3.84E-04
E.M. Asefa et al.

Toxicology Reports 12 (2024) 622–630
628
the country, indicating an uneven spatial distribution of OCPs. Addi-
tionally, insufcient temporal OCP data limited the detailed analysis of
changes in OCP concentrations before and after the implementation of
bans in Ethiopia. Thus, we were unable to conduct a detailed spatial and
temporal analysis of OCPs in Ethiopian waters. However, despite the
need for additional monitoring efforts, the analysis of OCP concentra-
tions presented in this study provides valuable insights into the existing
contamination status of Ethiopian water matrices concerning legacy
pesticides. We found that OCPs are more concerning than current-use
pesticides (CUPs) in terms of their concentrations and associated risks.
Evidence of bioaccumulation and biomagnication was also found in
this study. Overall, our ndings were consistent with similar studies
conducted elsewhere [11,12,32,52–55,64,83].
Although the exact sources of OCPs in Ethiopian waters were not
reported in the included studies, previous research has identied non-
point agricultural sources and vector-borne controls as primary sour-
ces. In Ethiopia, until very recently, OCPs such as DDT and endosulfan
were locally manufactured by Adami Tulu Pesticide Processing Share
Company. Despite some recent efforts made by the Environmental
Protection Authority (EPA) and Ministry of Health (MoH) to dispose
DDT and ban and restriction of the use of DDT and Endosulfan; Debela
et al.[13] showed that hundreds and thousands of DDT are stored in the
company’s warehouse, and there are approximately 460 sites suspected
to be contaminated with DDT. Furthermore, stockpiles of obsolete pes-
ticides are widely spread throughout the entire country, which can be an
important source of contamination in Ethiopian water [14,25,38].
Therefore, although our ndings showed the historical use of DDT in
Ethiopia, the recent input from the ongoing illegal use of OCPs, as well
as leaching from obsolete pesticide stocks, could explain the high con-
centrations reported in this study.
Although this study did not observe any health risks associated with
DDT exposure through drinking water, we did identify a signicant
health risk concern for the general Ethiopian population related to sh
consumption, with varying risks depending on the sh species
consumed. It is important to note that this study focused on DDT as a
representative OCP compound for health risk assessment and did not
consider the cumulative effects of multiple OCP exposures, although
these approaches are highly recommended for risk assessments [51,77].
Furthermore, the assessment assumed hypothetical exposure scenarios
and did not account for potential hotspots or localized areas with higher
contamination levels. Therefore, these results should be interpreted with
caution and considered as a preliminary assessment of the potential
health risks associated with OCP exposure in Ethiopia until further
studies explore the risks in more detail.
In conclusion, our ndings demonstrate ongoing concerns regarding
OCPs in various water matrices in Ethiopia, as evidenced by their high
concentrations, ability to bioaccumulate and biomagnify, and the health
risks posed through dietary exposures. However, due to the scarcity of
data and signicant heterogeneity among the matrices analyzed, it is
difcult to draw clear conclusions about the spatiotemporal trends of
OCPs in Ethiopia. These ndings emphasize the need for ongoing
monitoring and assessment of OCP contamination in Ethiopian waters,
with particular attention to understanding the dynamics across varying
space and time domains. Furthermore, given the continued concerns
regarding OCPs, it is crucial to re-evaluate regulations on their use and
promote sustainable agricultural and environmental management
practices to mitigate the release of these compounds.
Funding
This research did not receive any specic grant from funding
agencies in the public, commercial, or not-for-prot sectors.
CRediT authorship contribution statement
Roba Argaw Tessema: Writing – review & editing, Methodology.
Jerry Enoe: Writing – review & editing, Methodology. J´
ozef Ober:
Writing – review & editing, Methodology. Berhan M. Teklu: Writing –
review & editing, Validation. Ermias Deribe Woldemariam: Writing –
review & editing, Validation, Supervision. Elsai Mati Asefa: Writing –
review & editing, Writing – original draft, Visualization, Software,
Methodology, Investigation, Formal analysis, Data curation, Conceptu-
alization. Mekuria Teshome Mergia: Writing – review & editing,
Validation, Supervision, Project administration, Methodology, Data
curation, Conceptualization. Yohannes Tefera Damtew: Writing – re-
view & editing, Visualization, Supervision, Software, Methodology,
Formal analysis. Dechasa Adare Mengistu: Writing – review & editing,
Validation. Faye Fekede Dugusa: Writing – original draft, Supervision,
Methodology, Formal analysis, Data curation.
Declaration of Competing Interest
The authors declare that they have no known competing nancial
interests or personal relationships that could have appeared to inuence
the work reported in this paper.
Data Availability
Data will be made available on request.
Appendix A. Supporting information
Supplementary data associated with this article can be found in the
online version at doi:10.1016/j.toxrep.2024.06.001.
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