Making the Invisible Visible? Using Stable Isotope Analysis to Detect Indirect Toxicant Effects

Area of Science:

• Ecotoxicology
• Environmental Chemistry
• Ecological Research

Background:

• Stable isotope analysis (SIA) is a common ecological tool, but its use in ecotoxicology is limited due to concerns about chemical stressors affecting organism isotope signatures.
• Previous studies suggest toxicants may alter an organism's isotopic signature, raising questions about SIA's reliability in contaminated food webs.

Purpose of the Study:

• To investigate if the neonicotinoid thiacloprid alters trophic enrichment factors (TEFs) in the amphipod Gammarus fossarum.
• To determine if SIA can accurately track indirect toxicant effects on diet composition by comparing SIA-derived proportions with direct consumption observations.

Main Methods:

• Gammarus fossarum were exposed to varying concentrations of thiacloprid (0, 0.75, 5 µg L⁻¹) and fed specific diets (black alder leaves or Baetis rhodani larvae) for 6 weeks to assess TEF alterations.
• In a separate experiment, gammarids were exposed to two thiacloprid levels (0 and 0.75 µg L⁻¹) and fed mixed diets for 2 weeks to compare SIA-based dietary proportions with direct consumption data.

Main Results:

• Thiacloprid exposure caused statistically significant, yet minor, changes in TEFs, which were less influential than factors like resource quality or consumer condition.
• SIA-derived dietary proportions closely matched those obtained from direct observation of consumption, validating SIA's ability to detect dietary shifts.

Conclusions:

• SIA is a robust tool for detecting indirect toxicant effects on organism diets, particularly when TEFs are evaluated concurrently.
• The findings support the continued application of SIA in ecotoxicological studies, even in the presence of chemical stressors like thiacloprid.