A Meta-Analysis Evaluating the Relationship between Aquatic Contaminants and Chironomid Larval Deformities in Laboratory Studies

Chironomid larval deformities have been widely investigated as an aquatic pollution toxicity end point. Field chironomid surveys often show a spatial association between contaminants and deformities, suggesting contaminants cause deformities. However, over 40 years of laboratory assays have not been able to confirm this causality. We therefore conducted a review of the literature and meta-analysis, in order to (A) assess whether trends across assays indicated dose–response effects, (B) characterize the consistency of results, and (C) investigate whether experimental issues and publication bias were contributing to inconsistency and/or reducing confidence in results. The experimental issues we investigated were extraneous nonchemical laboratory stressors (which may mask or interact with chemical effects), and mortality (which can confound deformity results). Our meta-analysis of the most commonly tested chemicals suggested dose–response effects for copper, but not lead or zinc. However, we also found substantial inconsistency across studies. Both mortality and extraneous stressors were potentially contributing to this inconsistency, reducing confidence in most published data. We observed no evidence of publication bias. We conclude that any causal link between contaminants and deformities remains uncertain, and suggest improved experimental and data reporting procedures to better assess this relationship

Morphometric parameters and numbers of sand flathead captured at each sampling station in Port Phillip Bay.

<p>Superscript letters indicate homogeneous subsets for each variable (α = 0.05). All values are presented as means ± SEM.</p

Biomarker levels measured in sand flathead collected at 6 sites in Port Philip Bay, Australia.

<p>Superscript letters indicate homogeneous subsets for each variable (α = 0.05). All values are presented as means ± 95% confidence interval about the geometric mean.</p

Factor loadings and individual % variance for derived components (eigenvalues > 1.0) issued from PCA analysis.

<p>Factor loadings and individual % variance for derived components (eigenvalues > 1.0) issued from PCA analysis.</p

Principal Component Analysis plot.

<p>Principal Component 1 (biomarkers of exposure: biliary PAH metabolites) versus Principal Component 2 (biomarkers of effect: DNA damage, LSI and CF) provide a discrimination along Principal Component 2, between the low population density sites of Sorrento and St. Leonards (circles), and the highly industrialised/urbanised sites of Mordialloc, Hobson Bay and Corio Bay (squares).</p