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Biodynamic modelling of toxic metal accumulation by the lugworm Arenicola marina, a keynote deposit feeding polychaete in European estuaries: ecotoxicological and regulatory implications

Final Report Summary - DYNOLUG (Biodynamic modelling of toxic metal accumulation by the lugworm Arenicola marina, a keynote deposit feeding polychaete in European estuaries ...)

The DYNOLUG project tried to provide new insights on the exposure and effects of metals from sediments using the common lugworm, Arenicola marina, as model organisms living and feeding on sediments. The specific objectives of the project were:

- Development of a model to estimate metal bioaccumulation in lugworms. This was done by estimating empirically the kinetic parameters that describe metal uptake and elimination of essential (Zn) and non essential (Cd, Ag and As) metals from solution and diet (sediment). The values obtained for these parameters were then used to run a kinetic multi-pathway model together with information on the feeding rate and the chemical concentrations in the exposure media (water and diet).

- Model the metabolically available (and potentially toxic) metal fraction, by studying the subcellular compartmentalisation of accumulated trace metals in animals exposed in the laboratory to sediments with high metal concentrations causing different levels of toxicity.

The model, combined with geochemical analyses from a site of interest (i.e. metal concentrations and organic matter content in ingested sediment), was able to accurately predict bioaccumulated metal concentrations in natural populations of this species leaving in United Kingdom estuaries with different levels of metal contamination. The model also showed good results for modelling metal accumulation under laboratory exposures, showing that it is useful for predicting metal concentrations at steady-state in field-populations, but can be used as well to describe metal accumulation under hypothetical scenarios.

In our toxicity experiments the worms showed lower total accumulated metal concentrations just before mortality occurred (< 20 days) at the lethal exposure, than after 30 days of exposure to sediments not causing mortality. Moreover rates of accumulation of As, Cu and Zn were significantly higher in the lethal exposure than in the sublethal exposure. Our results showed that it is not possible to link mortality to a critical total body concentration, and we add to a growing body of literature indicating that metal toxicity occurs when organisms cannot cope with overwhelming influx and subsequent accumulation rates.

The lack of correlation of bioaccumulated concentrations with toxicity in aquatic invertebrates results from the detoxified storage of a significant proportion of the accumulated metal in the body. To test this hypothesis we measured the metal concentrations accumulated in different subcellular fractions in the worms under different levels of toxicity, observing that there may be a threshold concentration of metal in the not-detoxified fraction that, after being exceeded, triggers toxicity. This not-detoxified fraction was defined as that accumulated in organelles, heat-sensitive proteins and cellular debris. This hypothesis was supported with results from laboratory exposures of lugworms to sediments spiked with high concentrations of each of the individual metals (As, Cu and Zn) and with a mixture of the three.

The DYNOLUG project has provided risk assessors and decision-makers with a model that can be used for the study of exposure and effects of metals in sediments. This will represent a cost-effective method in time and costs for screening purposes. The model can also be used for sediment quality assessment, for example in pre-dredging characterisations required by the international conventions for the prevention of marine pollution.

The results also contribute towards a growing body of evidence suggesting that total metal concentrations in an animal is not a good predictor of toxicity, unless detoxification mechanisms are taken into consideration. The results should contribute to the more effective implementation of environmental quality standards for different purposes, for example those acclaimed for sediments in the Water Framework Directive, for dredged material management following international recommendations.

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