Toxicokinetic studies reveal variability in earthworm pollutant handling

A frequent characteristic of earthworms collected from contaminated sites is that they show considerable variation in measured tissue chemical concentrations. What is not certain is whether this variation results from local scale heterogeneity in soil concentrations and associated variation in exposure or rather from systematic and biologically based differences in earthworm pollutant handling. To assess patterns of earthworm chemical uptake and associated variation, accumulation was investigated in two bespoke toxicokinetic studies with the organic chemicals chlorpyrifos and fluoranthene and in a reanalysis of two published toxicokinetic studies with the metals Pb and Cd. The analysis of all data-sets highlighted extensive variation around one compartment model fits. Such consistently high variability, despite the homogenous nature of exposure within the test systems, hints at extensive biological variation in earthworms within the pathways involved in pollutant handling (uptake, metabolism, excretion) which goes beyond the simple methodological variation of a single test. The identified variation between individuals has important implications in areas such as biomarker analyses and secondary poisoning assessment. Further it indicates the presence of substantive selectable variation in pollutant handling that could support the development of pollutant tolerance in earthworms.