Body size-dependent Cd accumulation in the zebra mussel Dreissena polymorpha from different routes

- Cd accumulation in zebra mussels was negatively correlated with tissue weight.
- Size-dependent Cd bioaccumulation (Cd allometry) was dependent on exposure routes.
- Algal/water-Cd was more important than sediment-Cd in controlling Cd allometry.
- Importance of algal/water-Cd to Cd bioaccumulation varies with tissue weight.
- Size-dependent Cd uptake from various routes should be considered in biomonitoring.

Understanding body size-dependent metal accumulation in aquatic organisms (i.e., metal allometry) is critical in interpreting biomonitoring data. While growth has received the most attention, little is known about controls of metal exposure routes on metal allometry. Here, size-dependent Cd accumulation in zebra mussels (Dreissena polymorpha) from different routes were investigated by exposing mussels to A.(111Cd spiked algae+113Cd spiked river water) or B.(111Cd spiked sediments+113Cd spiked river water). After exposure, 111Cd or 113Cd levels in mussel tissue were found to be negatively correlated with tissue weight, while Cd allometry coefficients (b values) were dependent on Cd exposure routes: −0.664 for algae, −0.241 for sediments and −0.379 for river water, compared to −0.582 in un-exposed mussels. By comparing different Cd exposure routes, we found that size-dependent Cd bioaccumulation from algae or river water could be more responsible for the overall size-dependent Cd accumulation in mussels, and the relative importance of the two sources was dependent on mussel size ranges: Cadmium obtained from algae (algae-Cd) was more important in size-dependent Cd accumulation in smaller mussels (tissue dry weight < 5 mg), while river water-Cd became more important in larger individuals (tissue dry weight > 5 mg). In contrast, sediment-Cd contributed only a small amount to Cd accumulation in zebra mussels and may have little effect on size-dependent Cd bioaccumulation. Our results suggest that size-dependent Cd accumulation in mussels could be largely affected by exposure routes, which should be considered when trying to interpret Cd biomonitoring data of zebra mussels.

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