ABSTRACT
This review provides an overview of the role, routes and effects of manganese in aquatic crustaceans. Manganese is a naturally abundant metal in marine and freshwater sediments where it is involved in a large number of chemical processes. Although sediments contain high natural concentrations of manganese, the potential danger to benthic organisms has been neglected in studies to date. Manganese bioavailability increases as the result of human impact and it accumulates in biota. Manganese may occur in toxic concentrations (10-20 mg l
) in the bottom water of marine coastal areas after hypoxia, or more locally (e.g., close to industries) as well as in acidic lakes and aquaculture shrimp ponds. Though manganese is an essential metal, it is also an unforeseen toxic metal in the aquatic environment. Although the uptake and elimination of manganese is rapid, manganese affects processes that decrease the fitness of organisms. As manganese bioavailability increases, its uptake is predominately through the water. The midgut gland, nerve tissue, blood proteins and parts of the reproductive organs have the highest accumulation factors and are the main target tissues. The functional effects of manganese in aquatic environments are still sparsely investigated. Recent results show that the immune system, the perception of food via chemosensory organs and a normal muscle extension are affected at manganese concentrations observed in the field.
Manganese is the 12th most common element, the fourth most abundant metal and is universally distributed in the earth’s crust and waters (Anonymous 2005). This metal is involved in a large number of chemical processes, due mainly to its redox sensitivity. The literature on manganese (Mn) geochemistry in the aquatic environment is immense (Elderfield 1976), whereas literature on the occurrence and biological effects of manganese in aquatic animals is comparatively sparse. Manganese concentrations in soil vary from 0.001-7 mg g
