Ranked effects of heavy metals on marine bivalves in laboratory mesocosms: A meta-analysis

Highlights: • Lead and mercury were the most toxic heavy metals to bivalves. • Copper and cadmium were the most frequently studied heavy metals. • Essential heavy metals (Cu, Zn, Cd) do not necessarily exhibit lower toxicity. • Duration and concentration of exposure did not have a clear effect on toxicity. • Cellular level effect sizes were larger than physiological/population effects. - Abstract: Bivalves are commonly used as biomonitors for heavy metal pollution in marine environments because they accumulate heavy metal ions quickly, are sessile, abundant, and widely dispersed, and adult mortality from contamination is rare. However, the breadth of experiments used to measure the effect of heavy metal contamination can obscure general trends. It is unclear which heavy metals cause the most severe effects, how severity varies with exposure concentration and duration, and whether effects vary with level of biological organization. I conducted a meta-analysis of 48 mesocosm studies on the effects of heavy metal ions – silver, cadmium, copper, mercury, lead, and zinc – on marine bivalves. The ordering of effect sizes was Pb > Hg > Cu > Zn > Cd > Ag. The significance and direction of concentration and duration as moderators depended on the metal and the biological level. Future studies should consider non-linear effects over time and concentration, and measure both bioaccumulation and effect of the metals being studies.