Flow cytometry as a tool to monitor the disturbance of phagocytosis in theclam Mya arenaria hemocytes following in vitro exposure to heavy metals.

The effectiveness of toxicology biomonitoring programs could be improved by the addition of sensitive biomarkers. In this study the cell viability and sensitivity of phagocytic function of phagocytes from bivalves (Mya arenar ia) to selected heavy metals were measured by flow cytometry, a novel appro ach. Hemocytes (phagocytes) collected from bivalves by puncture of the post erior adductor muscle were incubated in vitro for 18 h in hemolymph contain ing 10(-9)-10(-3) M of cadmium chloride, zinc chloride, mercuric chloride, methylmercury chloride or silver nitrate, before determining their capacity to phagocytose fluorescent latex beads by;flow cytometry. Heterogeneity of the hemocyte cell population was determined by forward scatter (FSC) and s ide scatter (SSC) cytometric profile which showed two distinct cell populat ions. At low doses (10(-9), 10(-8) M), all the metal compounds studied stim ulated phagocytic activity except silver nitrate. At higher levels of expos ure (10(-6), 10(7) M), all metals caused a significant concentration-relate d decrease in hemocyte phagocytosis activity. From the concentration of eac h metal inducing 50% suppression (IC50) of the phagocytic activity, the imm unotoxic potential of metals with respect to phagocytic function can be ran ked in the following increasing order: ZnCl2 < CdCl2 < AgNO3 < HgCl2 < CH3H gCl. Parallel analysis of hemocyte viability showed that suppression of pha gocytosis by heavy metals was not solely related to a. decreased cell viabi lity. These results reveal the high but different degree of sensitivity of the phagocytosis activity of bivalves with respect to heavy metals, as meas ured by flow cytometry, and demonstrate that flow cytometry is a potentiall y useful tool in ecotoxicological monitoring. (C) 2000 Elsevier Science Ire land Ltd. All rights reserved.