Acute and chronic effects of water quality criteria‐based metal mixtures on three aquatic species

Abstract

AbstractAcute and chronic toxicity tests were conducted with three aquatic species to determine the effects of metals combined as mixtures at proposed water quality criteria concentrations and at multiples of the LC50 and maximum acceptable toxicant concentration (MATC) obtained from tests on six metals. These studies were the first part of a larger research effort to derive water quality criteria for combined pollutants by the U.S. Environmental Protection Agency.Arsenic, cadmium, chromium, copper, mercury and lead combined at criterion maximum concentrations caused nearly 100% mortality in rainbow trout and daphnids (Ceriodaphnia dubia) during acute exposures. Fathead minnows were not adversely affected at this or two times this concentration, although a mixture of four to eight times the maximum value caused 15 to 60% mortality. Metals combined at the criterion average concentrations significantly reduced production of daphnid young and growth of fathead minnows after 7 and 32 d, respectively. Embryo hatchability and survival of rainbow trout were reduced at four times this criterion but not at the criterion average concentration.Acute tests with metals mixed at multiples of the LC50 indicated that the joint action of the metals was more than additive for fathead minnows and nearly strictly additive for daphnids, based on toxic units calculated from the individual components of the mixture. Chronic tests showed that the joint action was less than additive for fathead minnows but nearly strictly additive for daphnids, indicating that long‐term metal interactions may be different in fish than in lower invertebrates. Adverse effects were observed at mixture concentrations of one‐half to one‐third the MATC for fathead minnows and daphnids, respectively, suggesting that components of mixtures at or below no effect concentrations may contribute significantly to the toxicity of a mixture on a chronic basis. These results point out the need for additional studies to determine the type and degree of interaction of toxicants because single‐chemical water quality criteria may not sufficiently protect some species when other toxicants are also present.