Accumulation of arsenic from water and food by Littorina littoralis and Nucella lapillus

Abstract

The mechanism, and factors influencing the process of arsenic accumulation and elimination in a food chain [Fucus spiralis (L.) → Littorina littoralis (L.) → Nucella lapillus (L.)] were examined using the radioisotope ⁷⁴As. Organisms were collected during 1978 from the estuary of Restronguet. Creek in southwest England. Arsenate uptake by L. littoralis increased linearly with increasing external arsenate concentration up to ca. 500 μg 1^-1 but was independent at higher arsenate concentrations. Arsenic uptake by L. littoralis was suppressed by metabolic inhibition (potassium cyanide) and lowered salinity. At 26°C, arsenic uptake was twice that at 10°C. L. littoralis accumulated 1o times more arsenic from solution than N. lapillus. Approximately 91% of ⁷⁴As accumulated from water by L. littoralis was found in the soft tissues, especially the digestive gland and gonads, but in N. lapillus 85% was associated with the shell. Arsenate uptake was twice that of arsenite in L. littoralis. Phosphate at normal environmental levels (2.4 μM) did not influence the accumulation of arsenic by L. littoralis, although concentration-dependent inhibition of arsenic uptake was found between 8 and 17 μM. Compared with macroalgae, the marine snails exhibit a much greater ability for eliminating arsenic. In L. littoralis the elimination of ⁷⁴As absorbed from sea water occurred in three stages, each contining equal amounts of the initial ⁷⁴As pool, with biological half-lives of 4, 13 and 47 d. A biphasic pattern of elimination was found for food-labelled snails (L. littoralis and N. lapillus). The rapid compartment, contributing a third of the arsenic, had a half-life of 4 d, while that of the slow compartment was 12 to 13 d. Fed snails eliminated arsenic more rapidly and extensively than starved individuals. All arsenic in the tissues of the snails studied was available for exchange with that in the environment. The diet is by far the major source of arsenic in L. littoralis and N. lapillus, which appear equally efficient at assimilating arsenic from food.