Short-term lethal and sublethal atrazine effects on Litoditis marina: towards a nematode model for marine toxicity assessment?

Abstract

Organochlorine pesticides are still widely used in many regions of the world, despite their toxic properties to many organisms, including humans, and their high environmental persistence in waters and sediments. In order to properly assess contaminant effects across trophic levels in aquatic communities, the responses of different model organisms should be investigated. Particularly for marine benthic environments, relatively few model organisms for the assessment under controlled laboratory conditions of both lethal and sublethal effects are available. Here we investigate the use of a cryptic species of the free-living nematode Litoditis marina as a model organism for short-term tests of the impacts of contaminants, using the case of the herbicide atrazine. Its ease of culturing, short generation time and high fecundity render L. marina PmIII a good candidate to assess contaminant effects for both a rapid assessment of impacts and more detailed investigations of the mechanisms behind those effects. The LC50 of atrazine to adult L. marina PmIII was 3.3 ± 0.5 mg/L after a 5-day exposure, suggesting a comparatively higher sensitivity of this species compared to other aquatic invertebrate model species, mainly crustaceans. This LC50 was less than half the value after a 4-day exposure and was 22-fold lower than the 48 h LC50, demonstrating the importance of performing lethality tests for as long an exposure time as possible. Sublethal effects were observed at much lower atrazine concentrations and encompassed, from 0.8 mg/L onwards, impairment of life-history traits (reduced fecundity and extended egg deposition and development times) and population parameters (abundances of juveniles and adults, adult sex ratio). These sublethal effects were broadly consistent among different life-history traits and population parameters, but fecundity and the maximum abundances of juveniles, adults and total nematodes were the most sensitive response variables. We therefore suggest that an adequate assessment of sublethal contaminant effects on L. marina requires a combination of different life-history traits and population-level parameters. We conclude that L. marina PmIII is a suitable model species for ecotoxicological research encompassing both lethal and sublethal effects, and can as such contribute to environmental risk assessment in marine and estuarine systems.