Are the heavy metals cadmium and zinc regulated in freshwater prawns?

In the present study, an attempt to assess the heavy metal (Cd and Zn) regulating ability of the commercially important freshwater prawn Macrobrachium malcolmsonii (Milne Edwards) was made by exposing it to a range of dissolved concentrations of Cd and Zn for 22 days. The prawn tissues accumulated the nonessential heavy metal cadmium at all exposure levels (6.3 to 157 microg x liter-1) without any regulation. However, the prawns regulate their tissue concentration of the essential metal zinc to an approximately constant level when exposed to a wide range of dissolved zinc concentrations (26 to 653 microg x liter-1) until a threshold dissolved concentration (373 microg x liter-1) is reached when regulation collapses and net accumulation of Zn begins.