 A study of nine different bivalves with widespread distributions in tropical marine waters concluded that the mussel , Trichomya hirsuta , most nearly reflected in its tissues the level of heavy metals ( Pb , Cd , Cu , Zn , Co , Ni , and Ag ) in its environment . In this species there was a linear relationship between the sedimentary levels and the tissue concentration of all the metals except zinc . In the Persian Gulf , the Atlantic pearl @-@ oyster ( Pinctada radiata ) is considered to be a useful bioindicator of heavy metals . 
