ABSTRACT
The 91 elements with natural occurrence can be divided into four groups: elements that are present in biological material, trace elements, elements with ecotoxicological effects, and elements of minor environmental interest. The second and third groups contain five elements that are trace elements and at the same time have ecotoxicological effect, because they may be present in the environment in concentrations that are higher than required for their function as trace elements, which can give an ecotoxicological effect. These five elements are chromium, copper, nickel, selenium, and zinc. We distinguish between threshold and non-threshold agents. Threshold agents are needed in a certain concentration for the growth of organisms, but if the concentration is too high, they may be harmful for the environment. Non-threshold agents or gradual agents are harmful for the environment in practically any concentration. Eighteen elements require particular attention in environmental management due to their ecotoxicological effect (numbers in parentheses indicate numbers in the periodic table): aluminum (13), chromium (24), nickel (28), copper (29), zinc (30), arsenic (33), selenium (34), strontium (38), silver (47), cadmium (48), tin (50), antimony (51), tellurium (52), barium (56), mercury (80), thallium (81), lead (82), and bismuth (83). Four of these elements are treated in more detail in entries with the titles “Mercury,” “Lead,” “Cadmium,” and “Copper.” A short overview of the environmental and ecotoxicological problems of these 18 elements is given in the second section of this entry.
