A review of the lethal and sub-lethal effects of mercury on aquatic life

Abstract

100 scientific papers published between 1937 and 1976 have been reviewed as part of an attempt to assess the environmental significance of mercury in natural waters. In general, the lethal effects on aquatic life of both inorganic and organic mercury compounds appear at concentrations greater than 10 μg/L. Similarly, sub-lethal responses to inorganic mercury occur where concentrations are greater than 3 μg/L. Organic mercury is apparently more harmful, the corresponding concentration being greater than 0.1 μg/L. Aquatic algae and the larval stages of molluscs and crustaceans appeared to be the most sensitive organisms to mercury. The conclusions reached following investigations under controlled conditions in the laboratory do not necessarily apply in the natural environment and this is particularly true for mercury. Probably the most important factor to be considered is the form in which the mercury is present in the environment, since natural processes such as adsorption, precipitation, volatilisation, and complexation are likely to reduce the concentration of 'biologically available' mercury. In addition, antagonistic reactions may reduce its effect. On the other hand, it is recognised that synergistic reactions with other metals, changes in salinity and temperature, and even natural stress are likely to increase the harmful effects of mercury on the biota. However, on balance, it appears that the factors tending to increase the harmful effects of mercury on the aquatic environment are far outweighed by the natural processes which tend to decrease the concentrations of 'biologically available' mercury.