Including Mixtures in the Determination of Water Quality Criteria for Herbicides in Surface Water

Swiss Federal Institute for Aquatic Science and Technology (Eawag), Duebendorf, Switzerland.
Environmental Science and Technology (Impact Factor: 5.33). 02/2006; 40(2):426-35. DOI: 10.1021/es050239l
Source: PubMed


Monitoring programs throughout America and Europe have demonstrated the common occurrence of herbicides in surface water. Nevertheless, mixtures are rarely taken into account in water quality regulation. Taking mixtures into account is only feasible if the water quality criteria (WQC) of the single compounds are derived by a common and consistent methodology, which overcomes differences in data quality without settling on the lowest common denominator but making best use of all available data. In this paper, we present a method of defining a risk quotient for mixtures of herbicides with a similar mode of action (RQm). Consistent and comparable WQC are defined for single herbicides as a basis for the calculation of the RQm. Derived from the concentration addition model, the RQm can be expressed as the sum of the ratios of the measured environmental concentration and the WQC for each herbicide. The RQm should be less than one to ensure an acceptable risk to aquatic life. This approach has the advantage of being easy to calculate and communicate, and is proposed as a replacement for the current limit of 0.1 microg/L for herbicides in Switzerland. We illustrate the proposed approach on the example of five commonly applied herbicides (atrazine, simazine, terbuthylazine, isoproturon, and diuron). Their risk profile, i.e., the RQm as a function of time for one exemplary river, clearly shows that the single compounds rarely exceeded their individual WQC. However, the contribution of peaks of different seasonally applied herbicides, whose application periods partially overlap, together with the continuously emitted herbicides from nonagricultural use, results in the exceedance of the RQm threshold value of one upon several occasions.

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    • "7160 [3747; 10,578] 18,931 [15,973; 21,889] 319 [0; 1450] EOMI Eolimna minima 11,180 [4359; 18,006] 20,143 [12,881; 27,404] 47,812 [25,037; 70,591] 1318 [903; 1732] MAFO Mayamaea fossalis 596 [545; 648] 2434 [1978; 2889] 4307 [3644; 4966] 261 [28; 497] Table 3 Literature organisms EC 50 (nM) database for the 4 herbicides obtained from Chèvre et al. (2006) Concentrations (nM) "
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    ABSTRACT: Species sensitivity distributions (SSDs) are an important predictive tool in risk assessment. Usually, literature data are used to build SSDs that are mostly based on planktonic species. But, to get adequate protective thresholds for environmental communities, one could argue that SSD should be built on ecotoxicological data obtained from species found in the ecosystem that should be protected. This is particularly true when benthic algae are of concern. Due to the lack of literature data, building SSD on benthic microalgae is difficult. This paper aims in comparing SSDs, and thus protective thresholds (hazardous concentration that affects 5 % of the species of a community, HC5), built on ecotoxicological data obtained (1) from literature and (2) with specific bioassays on benthic diatoms from a lake. Thresholds were derived for protection against four herbicides separately and for a mixture of them. Sensitivity data obtained from literature were statistically lower than the specific data for all herbicides: Species tested in the literature were usually more sensitive (mainly chlorophytes), leading to more protective lower HC5. The HC5 thresholds (literature or specific) derived for protection against the mixture were also compared to the observed sensitivity of an assemblage of benthic diatom species exposed to an increasing range of herbicide mixture concentrations. We observed that one species within the assemblage (Fragilaria rumpens) was affected at a concentration below both the literature and the specific HC5 thresholds.
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    • "Both improving risk evaluation procedures and characterizing pesticide effects in aquatic environments require the consideration of the interactions of substances in mixtures, such as found in the environment. The flagrant lack of knowledge in this area has been recently stressed by many researchers (Brock et al. 2006; Chèvre et al. 2006; Knauert et al. 2009). Complementarily, the impacts of the detected substances have to be evaluated on selected living organisms or 'key biological indicators' as defined by the WFD. "
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    ABSTRACT: The use of a large array of organic and inorganic micropollutants has been leading to an increasing pollution of surface and ground waters (Schwarzenbach et al. 2006). Headwater streams are highly dynamic systems exposed to the transport and dilution of anthropogenic inputs from agricultural land use of their watershed, where periphytic microorganisms (biofilms) play a key role in river functioning. At the basis of these ecosystems, these complex communities composed of photosynthetic organisms (both eukaryotes and cyanobacteria), bacteria, and fungi significantly contribute to primary production, nutrient cycling, and biodiversity (Lear et al. 2012). Thus, biological impairment due to pollution may cause irremediable environmental damage.Improving pesticide assessment tools in surface waters is required to implement appropriate risk mitigation measures and ultimately contribute to the preservation or restoration of aquatic resources water quality. For this purpose, French regulations ...
    Full-text · Article · Sep 2014 · Environmental Science and Pollution Research
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    • "EC) obtained for a single substance or a mixture from bioassays with different species. They are mainly used as predictive models for risk assessment purposes, with a view to extrapolate a threshold that will protect most of the environmental species (Chèvre et al., 2006). This protective threshold is known as the Hazardous Concentration (HC), and is usually defined as that which affects 5% of the species (HC 5 ). "
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    ABSTRACT: Benthic diatoms evolved in a biofilm structure, at the interface between water and substrata. Biofilms can adsorb toxicants, such as herbicides, but little is known about the exposure of biofilm organisms, such as benthic diatoms, to these adsorbed herbicides. We assessed the sensitivity of 11 benthic diatoms species to 6 herbicides under both planktonic and benthic conditions using single-species bioassays. The concentration that reduced the growth rate of the population by 10% (EC10) and 50% (EC50), respectively, varied depending on the species, the herbicides, and the growth forms involved. As a general trend, the more hydrophobic the herbicide, the more species were found to be sensitive under benthic growth conditions. Statistical differences (alpha<5%) were observed between the sensitivities under planktonic and benthic growth conditions for many hydrophobic herbicides. A protective effect of the biofilm against herbicides was observed, and this tended to decrease (at both the EC10 and EC50 levels) with increasing hydrophobicity. The biofilm matrix appeared to control exposure to herbicides, and consequently their toxicity towards benthic diatoms. For metolachlor, terbutryn and irgarol, benthic thresholds derived from species sensitivity distributions were more protective than planktonic thresholds. For hydrophobic herbicides, deriving sensitivity thresholds from data obtained under benthic growth seems to offer a promising alternative.
    Full-text · Article · Jul 2013 · Science of The Total Environment
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