Accumulation and elimination kinetics of manganese from different tissues of the Norway lobster Nephrops norvegicus (L.)

Abstract

The exposure of marine benthic animals to dissolved manganese (Mn) occurs from metalliferous outlets or the enhanced flux of dissolved manganese from sediments during hypoxia. A prerequisite to valid interpretation of manganese concentrations measured in animals in situ is a thorough understanding of accumulation and elimination rates of this metal by relevant target tissues in organisms exposed to environmentally realistic manganese concentrations. Norway lobster, Nephrops norvegicus, accumulated manganese when exposed to solutions of <0.06 (background), 5 and 10 mg Mn l −1 for 20 days and was allowed to eliminate any accumulated manganese in undosed sea water for a further 20 days. During this period individual N. norvegicus were dissected into a number of components (brain, ventral ganglion, haemolymph, midgut gland, gills and exoskeleton) and the manganese concentration of each was analysed. Manganese accumulation reached a plateau after 1.25 days in all tissues except for midgut gland, which continued to accumulate manganese during the entire exposure period. In general, the manganese elimination was significantly slower than accumulation and reached a plateau after 1.25–2.5 days (except the gills) following exposure to clean sea water. The accumulation factor (AF), when compared to maximum concentrations in control and exposed animals, was highest in the haemolymph (×88) followed by nerve tissue (×22) at the 10 mg Mn l −1 exposure. The concentration factor (CF), when comparing manganese accumulation in tissues (wet weight) with exposure concentration, was 1.2–3.5 and for most tissues was similar for both exposure concentrations or slightly higher in the 5 mg Mn l −1 exposure—indicating net accumulation of manganese in all tissues with a saturation effect with increasing exposure concentrations. Thus, from these experiments it may be concluded that measured manganese concentrations in N. norvegicus give an indication of recent exposure to manganese concentrations in the bottom waters of their habitats.