Delineating metal accumulation pathways for marine invertebrates

Delineating the routes of metal uptake in marine invertebrates is important for understanding metal bioaccumulation and toxicity and for setting appro priate water and sediment quality criteria. Trace element biogeochemical cy cling can also be: affected if the rates of metal uptake and regeneration b y marine animals are dependent on the routes of metal accumulation. In this paper we review recent studies on the pathways of metal accumulation in ma rine invertebrates. Both food and water can dominate metal accumulation, de pending on the species, metal and food sources. Trace elements which exist in seawater primarily in anionic forms (e.g. As and Se) are mainly accumula ted from food. For metals that tend to associate with protein, uptake from water can be an important source. Kinetic modeling has recently been used t o quantitatively separate the pathways of metal uptake in a few marine inve rtebrates. This approach requires measurements of several physiological par ameters, including metal assimilation efficiencies (AE) from ingested food, metal uptake rates from the dissolved phase, and metal efflux rates (physi ological turnover rates) in animals. For suspension feeders such as mussels and copepods, uptake from the dissolved phase and food ingestion can be eq ually important to metal accumulation. Metal AE and partition coeffcients f or suspended particles, which are dependent on many environmental condition s, can critically affect the exposure pathways of metals. For marine surfac e deposit feeding polychaetes such as Nereis succinea, nearly all metals ar e obtained from ingestion of sediments, largely because of their high inges tion rates and low uptake from solution. The bioavailability of metals from food and the trophic transfer of metals must be considered in establishing water and sediment quality. (C) 1999 Elsevier Science B.V. All rights rese rved.