Shedding the load: Moulting as a cause of variability in whole-body metal concentrations

Moulting is a biological process shared by aquatic macroinvertebrates, but while the exoskeleton is believed to be a major sink of metal pollutants, the contribution of the moulting of the crustacean exoskeleton to total accumulated metal concentrations is insufficiently considered. We present a conceptual, qualitative model that illustrates the impact of moulting on the whole-body burden of an unspecified metal analyte in a hypothetical moulting invertebrate. The model demonstrates that moult stage is a contributor to the whole-body pollutant concentration, and that this introduces a temporal component even in steady-state exposure conditions. The applicability of this model is illustrated by comparison to published results of pre- and post-moult accumulations. A solution for reducing this variability in the measurement of whole-body metal concentrations is presented, and its potential application to both ex-situ and in-situ studies of biomonitor species is discussed.