Once free in the system, lead may cause nephrotoxicity, neurotoxicity, and hypertension. When mercury enters water it is often transformed by microorganisms into the toxic methyl mercury form. Symptoms of acute poisoning are pharyngitis, gasteroenteritis, vomiting, nephritis, hepatitus, and circulatory collapse. The presence of abundant chromium anions in the water is generally a result of industrial waste. Aquatic organisms may be adversely affected by heavy metals in the environment.
Many organisms are able to regulate the metal concentrations in their tissues.
Fish and crustacea can excrete essential metals, such as copper, zinc, and iron, that are present in excess. Thus, bivalves tend to suffer from metal accumulation in polluted environments. Shellfishing waters are closed if metal levels make shellfish unfit for human consumption. In comparison to freshwater fish and invertebrates, aquatic plants are equally or less sensitive to cadmium, copper, lead, mercury, nickel, and zinc. Metal uptake rates will vary according to the organism and the metal in question.