Biology session

Contaminants derived from agricultural areas that get into natural water bodies have considerable environmental impacts and can cause lethal and sublethal effects in non-target organisms, including wildlife and humans. In this study, we investigated the herbicide terbuthylazine that is used in agriculture worldwide and in Hungary as well. The herbicide atrazine which has similar structure to therbuthylazine is banned in the European Union, because several studies suggest it is an endocrine disruptor and can affect amphibians’ development rate and immune system, and it can cause decreased body mass, hyperactivity, and female-biased sex ratio. However, the ecotoxicological effects of terbuthylazine are poorly known. We exposed two anuran species throughout their larval development to each of two environmentally relevant concentrations of terbuthylazine (0,3 μg/L and 3 ng/L; the control group received 1 μl/L ethanol as solvent control), and we recorded several sub-lethal endpoints that are relevant for fitness in nature.

In common toads (Bufo bufo), we found that treatment with 0.003 µg/L terbuthylazine increased body mass at metamorphosis, but treatment with 0.3 µg/L terbuthylazine had no effect on body mass. In agile frogs (Rana dalmatina), treatment with 0.3 µg/L terbuthylazine decreased tadpole activity; this result contradicts the previously reported effects of atrazine. Reduced activity may have deleterious effects in nature: in competition for limited food it may put these individuals at a disadvantage, and predation risk may increase if the animals respond to the predators too slowly. The prevalence of polysplenia, and the spleen's size and pigmentation were not affected by the treatments, although in agile frogs we found that treatment with the higher concentration decreased spleen size by 12% (a marginally non-significant effect). Neither treatments affected the time to metamorphosis or sex ratios significantly, although in agile frogs the proportion of males increased from 44,6% in the control group to 57% in the low-concentration treatment. Unequal sex ratio is a threat to the survival of the population especially in taxa like anurans which have limited dispersal.

These results show that environmental levels of terbuthylazine can have several sub-lethal effects on anurans, which may be harmful to individual fitness and population persistence in natural conditions. Our experiment highlights that toxic effects cannot be generalized between chemicals of similar structure, because the terbuthylazine effects we observed do not conform with previously reported effects of atrazine. Therefore, it is important to study the ecotoxicological effects of every pesticide.