Impact of Tetrachloroethylene on Groundwater Ecosystems: Sub-Chronic Effects on the Locomotion Behavior of Two Harpacticoid Copepod Species

Aliphatic chlorinated hydrocarbons, particularly tetrachloroethylene (also known as perchloroethylene, PCE), persist as significant groundwater contaminants, often exceeding safe drinking water thresholds. This study fine-tunes the groundwater risk assessment of PCE on the sensitivity of groundwater-obligate (stygobitic) species. Through sub-chronic exposure trials on two copepod species, the stygobitic Moraria sp. and the non-stygobitic Bryocamptus zschokkei, we challenged the current European Predicted No-Effect Concentration (PNEC) of PCE in groundwater. Specifically, we applied a correction factor of 1000 to the current PNEC of PCE in water (50 ng/L PCE) and investigated the sub-chronic effects on the locomotion traits of the adult females of the two species. We used TrAQ, a MATLAB-based software developed by the University of L'Aquila. The software, designed for two-dimensional tracking of unmarked single animals video recorded in Open Field tests, is free and can be adapted to various 2D behavioral assessments with no need for dedicated hardware. Our findings revealed significant locomotion impairments in both species at a concentration of 50 ng/L PCE, suggesting the inadequacy of the existing European groundwater risk assessment procedures. Bryocamptus zschokkei exhibited particularly high mortality rates and persistent post-exposure impairments. The absence of recovery after PCE clearance in B. zschokkei underscores its higher susceptibility to PCE compared to Moraria sp., potentially due to differences in metabolic rates. This finding highlights the potential of B. zschokkei as a surrogate species for groundwater risk assessment. We advocate for refining groundwater risk assessment methodologies to better account for the vulnerabilities of stygobitic species.