Development of biomarkers in the earthworm Aporrectodea caliginosa for biological and ecological monitoring

Abstract

Biomarkers have been used for routine environmental monitoring and have the potential to play an important role in ecological risk assessment. The biomarker approach considers the toxicity of chemicals in the field in a different manner from the classical methods by measuring the effect that exposure to the chemical has on the organism. This research targeted two areas of environmental contamination - agroecosystems and industrial contaminated sites - by developing biomarkers for detecting exposure to two organophosphates, diazinon and chlorpyrifos, and to polycyclic aromatic hydrocarbons (PAHs) and other industrial contaminants.

Cholinesterase (ChE) activity and the neutral red retention assay (NRRA) were sensitive to simulated field rates of diazinon and chlorpyrifos in the laboratory, but glutathione Stransferase activity proved insensitive to induction by these pesticides. The NRRA was sufficiently, sensitive to detect exposure to these pesticides at recommended field rates, while inhibition of ChE activity was detected only at artificially high field rates. However, ChE activity was reduced in the absence of any effects on abundance, indicating that ChE activity is a more sensitive indicator of exposure than is abundance, and therefore may have a role in detecting overuse/abuse of these pesticides.

To further clarify the lack of effects of diazinon and chlorpyrifos in the field, the effects of these pesticides on life-table parameters in juveniles and adults was determined in the laboratory, and compared with biomarker responses. Juvenile maturation was less sensitive to pesticide exposure than was cocoon production. Growth and cocoon production in earthworms exposed as juveniles was more sensitive than these parameters in earthworms exposed as adults. Life-table responses in juveniles may, therefore, be more predictive of long-term impacts of organophosphates on populations than responses in adults. Impacts of diazinon and chlorpyrifos exposure on ChE activity and the NRRA occurred at similar or lower concentrations than those causing adverse impacts on growth and fecundity in the earthworms, indicating that these two biomarkers can provide some early warning of subsequent toxicity of these organophosphorous insecticides.

Three biomarkers, cytochrome P450 activity, the NRRA, and avoidance behaviour were evaluated as potential indicators of exposure for evaluation of contaminated sites. Cytochrome P450 activity proved to be non-inducible in earthworms exposed to benzo[a]pyrene, a common contaminant in New Zealand contaminated sites, and was deemed not useful as a biomarker in earthworms.

The NRRA proved to be a sensitive biomarker of exposure for detecting field-relevant concentrations of PAHs and other industrial contaminants, and was more responsive than effects on growth or fecundity. This assay can therefore be used as an early warning indicator to predict subsequent adverse impacts of exposure to contaminated soils and to determine potential impacts on earthworm populations.

The earthworm avoidance behaviour bioassay was also very sensitive and results were predictive of those obtained for chronic toxicity tests. Therefore, avoidance behaviour in this species may be useful for predicting potential detrimental ecological impacts at contaminated sites in New Zealand, and could be used as a simple pre-screening test for evaluation of contaminated soils prior to more extensive testing.