Abstract
Anthropogenic pressure such as agricultural pollution globally affects amphibian populations. In this study, a total of 178 different compounds from five agrochemical groups (i.e. antimicrobial drugs residues (ADRs), coccidiostats and anthelmintics, heavy metals, mycotoxins and pesticides) were determined monthly, from March until June 2019 in 26 amphibian breeding ponds in Flanders, Belgium. Furthermore, a possible correlation between the number and concentration of selected contaminants that were found and the percentage of arable land within a 200 m radius was studied. Within each group, the highest detected concentrations were obtained for 4-epioxytetracycline (0.422 μg L-1), levamisole (0.550 μg L-1), zinc (333.1 μg L-1), 3-acetyldeoxynivalenol (0.013 μg L-1), and terbuthylazine (38.7 μg L-1), respectively, with detection frequencies ranging from 1 (i.e. 3-acetyldeoxynivalenol) to 26 (i.e. zinc) out of 26 ponds. Based on reported acute and chronic ecotoxicological endpoints, detected concentrations of bifenthrin, cadmium, copper, cypermethrin, hexachlorobenzene, mercury, terbuthylazine, and zinc pose a substantial ecological risk to aquatic invertebrates such as Daphnia magna and Ceriodaphnia dubia, which both play a role in the food web and potentially in amphibian disease dynamics. Additionally, the detected concentrations of copper were high enough to exert chronic toxicity in the gray treefrog (Hyla versicolor). The number of detected compounds per pond ranged between 0 and 5 (ADRs), 0 - 2 (coccidiostats and anthelmintics), 1 - 7 (heavy metals), 0 - 4 (mycotoxins), and 0 - 12 (pesticides) across the four months. Furthermore, no significant correlation was demonstrated between the number of detected compounds per pond, as well as the detected concentrations of 4-epioxytetracycline, levamisole, copper, zinc, enniatin B and terbuthylazine, and the percentage of arable land within a 200 m radius. For heavy metals and pesticides, the number of compounds per pond varied significantly between months. Conclusively, amphibian breeding ponds in Flanders were frequently contaminated with agrochemicals, yielding concentrations up to the high μg per liter level, regardless of the percentage surrounding arable land, however showing temporal variation for heavy metals and pesticides. This research also identifies potential hazardous substances which may be added to the European watch list (CD 2018/408/EC) in the future.
Highlights
Agrochemical use has become an important component of global agricultural systems for decades, allowing for significant increases in crop yields and food production necessary to meet the exponential growth of the worlds’ population (Carvalho, 2017)
Doxycycline was the most frequently detected antimicrobial drug residues (ADRs) with a prevalence in 10 out of 22 ponds found in June
As we demonstrated that the detected concentrations of certain heavy metals and pesticides exceeded the reported ecotoxicological endpoints for the aquatic invertebrate D. magna and the gray treefrog H. versicolor, posing a potential risk, it is suggested that measures to reduce pond water contamination primarily focus on these compounds
Summary
Agrochemical use has become an important component of global agricultural systems for decades, allowing for significant increases in crop yields and food production necessary to meet the exponential growth of the worlds’ population (Carvalho, 2017). Pesticides (i.e. fungicides, herbicides and insecticides) typically enter the aquatic environment by mechanisms of runoff, leaching and aerosol-mediated dispersion or drift, following their direct application to crops on land (Hasanuzzaman et al, 2019). Antimicrobial and antiparasitic drugs, such as anthelmintics and coccidiostats, are commonly used veterinary medicines, administered parenterally or orally to the individual animal, or procured as mass medication through feed or drinking water. As these compounds (and their in vivo metabolites) are excreted in feces and urine, they may enter surface waters through runoff from pastures or cropland amended with manure (Kim and Carlson, 2006)
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