The modulating role of salinity in herbicide toxicity to the marine nematode Litoditis marina

Abstract Estuarine ecosystems are highly dynamic, characterized by frequent fluctuations in salinity. These environments are also primary recipients of pesticide-laden runoff, such as those from the triazine group, which pose significant ecological risks. However, the interactive effects of these chemical and physical stressors are not yet fully understood. This study investigated the effects of salinity on atrazine toxicity. We used the estuarine nematode Litoditis marina , an ideal bioindicator species, in a fully crossed experiment. Mortality was assessed for 120 h across a range of salinity levels (15, 20, 25, and 30) and atrazine concentrations (0.2–20 mg/L). Atrazine lethality was significantly influenced by the exposure duration, salinity, and their interactions. Toxicity is inversely related to the salinity. Specifically, the LC 50 at a salinity of 15 was 0.66 ± 0.01 mg/L, which is 10.4 times lower (i.e., more toxic) than the LC 50 at a salinity of 30 (6.88 ± 0.64 mg/L). A similar pattern was observed for LC 20 , which was 9.2 times lower at a salinity of 15 compared with that at 30. Reduced salinity dramatically increased atrazine toxicity in L. marina . These findings suggest that estuarine organisms are particularly vulnerable to pesticide pollution because inherent salinity fluctuations in their environment can intensify the toxic effects of contaminants. This highlights the importance of considering environmental variables in ecological risk assessment.