Sensitivity of Ethiopian aquatic macroinvertebrates to the pesticides endosulfan and diazinon, compared to literature data
Ecotoxicology
Sensitivity of Ethiopian aquatic macroinvertebrates to the pesticides endosulfan and diazinon, compared to literature data
Berhan M. Teklu 0 1 2 3
Negussie Retta 0 1 2 3
Paul J. Van den Brink 0 1 2 3
0 College of Natural Sciences, University of Addis Ababa , 4 Kiklo Campus, Addis Ababa , Ethiopia
1 Department of Aquatic Ecology and Water Quality Management, Wageningen University, Wageningen University and Research centre , P.O. Box 47, 6700 AA Wageningen , The Netherlands
2 & Paul J. Van den Brink
3 Alterra, Wageningen University and Research centre , P.O. Box 47, 6700 AA Wageningen , The Netherlands
The aims of the present study were to present a methodology for toxicity tests that can be used when analytical resources to verify the test concentrations are limited, and to evaluate whether the sensitivity of a limited number of Ethiopian species to pesticides differs from literature values for, mainly, temperate species. Acute toxicity tests were performed using three Ethiopian aquatic invertebrate species, one crustacean (Diaphanosoma brachyurum) and two insects (Anopheles pharoensis and Culex pipiens) and using the pesticides endosulfan and diazinon. All species-pesticide combinations were tested in duplicate to estimate the consistency, i.e. the intra-laboratory variation, in test results. Daphnia magna was tested as well to allow the test results to be compared directly with values from the literature. Results indicate that the differences between the EC50s obtained for D. magna in this study and those reported in the literature were less than a factor of 2. This indicates that the methodology used is able to provide credible toxicity values. The results of the duplicated tests showed intra-laboratory variation in EC50
Single-species toxicity tests; Tropics; Ecological risk assessment; Species sensitivity distribution; Africa
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values of up to a factor of 3, with one test showing a
difference of a factor of 6 at 48 h. Comparison with
available literature results for arthropod species using
species sensitivity distributions indicated that the test
results obtained in this study fit well in the log-normal
distribution of the literature values. We conclude that the
methodology of performing multiple tests to check for
consistency of test results and performing tests with
D. magna for comparison with literature values to check
for accuracy is able to provide reliable effect threshold
levels and that the tested Ethiopian species did not differ in
sensitivity from the arthropod species reported on in the
literature.
Introduction
The current intensification of agricultural activities in
Ethiopia results in a steady increase in both the types and
quantities of agrochemicals
(Taddese and Asferachew
2008)
. Pesticides may, however, cause risks to aquatic
ecosystems through contamination by spray drift, run-off,
drainage and accidental spills. To prevent environmental
harm from the application of these agrochemicals, it is
essential to perform a prospective environmental risk
assessment before registering a pesticide
(Teklu et al.
2015)
. Estimating the risks of pesticides to the aquatic
ecosystem includes an effect assessment which is often
based on acute and chronic laboratory tests of the toxicity
of these compounds to aquatic species.
Brock et al. (2006)
noted the importance of acute toxicity tests with fish, algae
and invertebrates for the first tier in the risk assessment of
pesticides, in order to identify ecosystem components
whose sensitivity should be further evaluated in higher-tier
risk assessment procedures
(Van den Brink 2013)
. These
tests also help the retrospective chemical risk assessment,
by identifying species that are sensitive to pesticide
pollution, so that the presence or absence of a sensitive species
in an area may be an indication of the pollution status of
that particular area
(e.g. Wahizatul et al. 2011)
, although
the absence of a species may have other causes as well.
At present, such an assessment often depends on the
results of toxicity tests performed with temperate species,
as data on tropical species are scarce
(Kwok et al. 2007)
.
Risk assessments performed for tropical ecosystems
should be (partially) based on toxicity data for tropical
species, since differences in sensitivity might be expected
(Daam and Van den Brink 2010)
, although empirical data
suggest no systematic differences in sensitivity
(e.g.
Kwok et al. 2007; Rico et al. 2010)
. Gathering sensitivity
data for local species enables further examination of
whether European and North American data can be
extrapolated to other geographical areas
(Hose and Van
den Brink 2004; Maltby et al. 2005)
. Although Ethiopia is
located in the tropical region, the risk assessment for
pesticide registration is solely dependent on the available
temperate acute toxicity data
(Teklu et al. 2015)
. Only a
few toxicity tests have been performed with Ethiopian
species, one example being a study (...truncated)