ABSTRACT
The impact of potentially toxic chemicals on wildlife is commonly assessed by comparing the intake of the contaminant with the "no observable effects level" (NOAEL) of intake. It is known, however, that there are considerable uncertainties inherent in this method. This study presents a Monte-Carlo based model to assess the degree of risk posed to birds (dunlin, Calidris alpina) from important estuarine habitats, and to show the limitations of such risk assessments, particularly with regard to data availability. The model was applied to predict the uptake of metals (Hg, Pb) in this shorebird species in Poole Harbour and the Severn Estuary/Bristol Channel, UK, two internationally important shorebird habitats. The results show that in both areas, Pb and Hg concentrations may pose an ecologically relevant toxic risk to wading birds. For Pb, uncertainty in NOAEL values dominates the overall uncertainty. Use of lethal toxicity data (LD50/100) was investigated as a method for assessing sub-lethal impacts from Hg. It was found that this method led to a significant under-estimate of the potential impact of Hg contamination, compared with direct estimation of NOAEL.
Subject(s)
Charadriiformes/physiology , Environmental Exposure/adverse effects , Environmental Monitoring/methods , Metals, Heavy/toxicity , Rivers/chemistry , Water Pollutants, Chemical/toxicity , Animals , Food Chain , Lead Poisoning/etiology , Lead Poisoning/metabolism , Metals, Heavy/analysis , Metals, Heavy/metabolism , Methylmercury Compounds/analysis , Methylmercury Compounds/metabolism , Methylmercury Compounds/toxicity , Models, Statistical , Monte Carlo Method , No-Observed-Adverse-Effect Level , Reproduction/drug effects , Reproduction/physiology , Risk Assessment , United Kingdom , Water Pollutants, Chemical/analysis , Water Pollutants, Chemical/metabolismABSTRACT
In a number of extensive coastal areas in northwest Europe, large numbers of long-lived migrant birds eat shellfish that are also commercially harvested. Competition between birds and people for this resource often leads to conflicts between commercial and conservation interests. One policy to prevent shellfishing from harming birds is to ensure that enough food remains after harvesting to meet most or all of their energy demands. Using simulations with behaviour-based models of five areas, we show here that even leaving enough shellfish to meet 100% of the birds' demands may fail to ensure that birds survive in good condition. Up to almost eight times this amount is needed to protect them from being harmed by the shellfishery, even when the birds can consume other kinds of non-harvested prey.
