Enzymatic and histopathologic biomarkers as indicators of contaminant exposure and effect in Asian clam (Potamocorbula amurensis)

Enzymatic and histopathologic alterations of the digestive gland, gill, gon ad, and kidney were studied in Asian cram (Potamocorbula amurensis) in Apri l, 1997 from each of four United Stales Geological Survey (USGS) stations i n the San Francisco Estuary. Stations were selected based on differing body burdens of metallic contaminants in crams (Stn 4.1>6.1>8.1>12.5) observed over 7 years. Because no pristine sites are known within the estuary and be cause no laboratory-reared stocks of P. amurensis were available, clams fro m station 12.5 served as reference animals. Histopathologic analysis reveal ed no lesions in clams corrected from station 12.5. Mild digestive gland at rophy and moderate distal kidney tubular vacuolation were seen in clams col lected from station 8.1. Mild digestive gland atrophy, moderate kidney tubu lar atrophy, and moderate gill inflammation were seen in clams collected fr om station 6.1. Lesions found only in clams from station 4.1 were: (1) seve re inflammation and moderate atrophy of primary ducts and diverticula, and decreased numbers of heterophagosomes and heterolysosomes in diverticula of the digestive gland; (2) severe gill inflammation; (3) severe kidney tubul ar atrophy; (4) severe ovarian and testicular inflammation and necrosis; (5 ) decreased numbers of mature ova; and (6) decreased number of glycogen sto rage cells in the ovary and testis. Localization of specific enzymes includ ing adenosine triphosphatase (ATP), acid phosphatase (ACP), alkaline phosph atase (ALKP), gamma-glutamyl transpeptidase (GGT), and glucose-6-phosphate dehydrogenase (G6PDH) was performed and correlated, in serial sections with glycogen (PAS) and haematoxylin and eosin stains. Enzymatic analysis revea led: (1) increased digestive diverticula ATP in stations 6.1 and 4.1; (2) d ecreased digestive diverticula ACP in stations 6.1 and 4.1 and proximal kid ney tubular ACP deficiency in station 4.1; (3) no ALKP differences among st ations; (4) increased distal kidney tubular GGT at station 12.5 and decreas ed distal kidney tubular GGT at station 4.1; (5) decreased digestive divert icula G6PDH G6PDH in all stations except 12.5 and decreased proximal kidney tubular G6PDH in stations 8.1 and 6.1. It is possible that other anthropog enic and natural stressors may have affected the results in this study. How ever, the prevalence and increased severity of lesions in clams with highes t metal body burden suggests a contaminant-associated etiology. Enzymatic a nd histopathologic biomarker alterations identified in this study were posi tively correlated with the metal body burden. Crams with the higher prevale nce of diseases and enzyme alterations also showed a lower condition index and glycogen content in the month when histopathological assessment was per formed. Further study win seek to develop enzymatic and histopathologic bio markers for use in controlled laboratory conditions to help validate the fi eld study.