EFFECTS OF OIL AND CHEMICALLY DISPERSED OIL IN SEDIMENTS ON CLAMS1

Abstract

ABSTRACT Several field experiments with natural sediments in the intertidal zone were conducted over a two-year period to compare the effects of Prudhoe Bay crude oil and this same oil dispersed with Corexit® 9527 (1 part Corexit to 10 parts oil). The clams used were Protothaca staminea and Macoma inquinata. Exposure periods ranged from one to six months. In a one-month exposure to about 2,000 parts per million (ppm) total oil in sediments, survival of P. staminea was two to three times greater than that of M. inquinata, and both species exhibited lower tolerance to oil alone in sediment than dispersed oil at the same concentration. However, uptake of naphthalenes and phenanthrenes by M. inquinata was greater from sediments mixed with dispersed oil than oil alone. Dispersed oil in this 30-day exposure also produced a decrease (compared to field controls) in the concentration of some of the free amino acids in the tissues of M. inquinata. Four- and six-month field exposures of small P. staminea to sediment containing oil or dispersed oil (about 2,000 ppm) reduced growth in both oil treatments (four-month exposure) or in just the chemically dispersed oil treatment (six-month exposure). In the latter experiment initial petroleum concentrations in the surface sediments (top 3 centimeters) were higher (about 3,000 ppm) for the dispersed oil than for oil alone. Surface layers in both conditions were free of contamination (down to 6 cm) after six months.