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The ecotoxicology of Cadmium in fresh and sea water and water pollution with Cadmium in Denmark
Møhlenberg, F.; Jensen, A. (1980). The ecotoxicology of Cadmium in fresh and sea water and water pollution with Cadmium in Denmark. The National Agency of Environmental Protection: Copenhagen. 42 pp.

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    Archived ILVO collection: VLIZ Archive A.ILVO.38 [102447]


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  • Møhlenberg, F.
  • Jensen, A.

    Compared to most other heavy metals the affinity of cad- mium to natural particulates is low, especially in sea water. Therefore, in the open sea and in the oceans cadmium occurs in the dissolved form ( often more than 99%). In estuarine and other near shore waters, where the concentrations of particulate material are often much higher than in the oceans, up to 10-20% of cadmium is found adsorbed onto particulates. Fresh water and especially rivers and lakes in urban areas often contain high concentrations of suspended matter and in such areas most cadmium is bound to particulates. After mixing with sea water, as in estuaries, cadmium loses its affinity for particulate matter and most cadmium adsorbed onto particulates desorbs. Landbased discharges of cadmium reaching the sea either directly or via rivers therefore give rise to elevated concentrations of cadmium in the waters in the discharge areas. If the water exchange of the marine recipient is low, discharges of cadmium may lead to accumulation of cadmium in the water, and effects on the organism living there may occur. In fresh water, dissolved cadmium occurs predominantIy in the form of Cd2+ion. However, in certain waters Cd-humus complexes may dominate. As salinity increases, complexes between Cd and chloride ions account for more and more of the dissolved forms while the Cd2+ion becomes less and less dominant, reaching only about 2% of the dissolved forms at 35°/oo salinity. The concentration of cadmium in natural waters varies greatly. The "normal " range of concentrations in fresh water and near-shore sea water are 0.03-0.2 ug/l, in seas and oceans 0.01-0.1 ug/l. Levels above the "normal" concentrations indicate contamination with cadmium. Uptake by planktonic algae and zooplankton deplete cadmium (and phosphate and nitrate) in surface waters of seas and oceans. When faecal pellets from zooplankton settle through the water column, some cadmium (and phosphate and nitrate) will leach due to degradation of the membrane encapsulating the faecal pellets. This gives rise to increased concentrations of dissolved cadmium (and phosphate and nitrate) in deep waters. In upwelling areas, the dissolved cadmium returns to the surface waters. Not all cadmium is regenerated, and therefore some cadmium may accumulate in sediments, especially in areas of high productivity. In the sediment cadmium is mainly associated with small organic particles. High concentrations of cadmium are thus to be found in areas where rates of sedimentation of organic particles (e.g. faecal pellets of zooplankton) are considerable. Therefore, high concentrations in the sediment do not need to be the result of a cadmium discharge, but may be the result of substantial sedimentation of organic matter . However, in discharge areas the correlation between cadmium and organic matter in the sediment may not be valid. Dissolved cadmium (and probably only the Cd2+ion) is taken up by algae and suspension feeders. In organisms located higher in the marine food chains uptake via food dominates. In fresh water, however, uptake from water may be significant also in fish, due to a high proportion of the accumulable Cd2+ion. Most aquatic animals concentrate cadmium in liver or digestive gland and kidneys, where cadmium is most often detoxicated due to binding to a low molecular weight protein, metallothionein. This protein is synthesized in response to cadmium exposure. On the basis of whole animal analyses, biomagnification is not evident, but can be found when specific organs are analysed. Among marine organisms, molluscs accumulate cadmium to the greatest extent and are therefore widely used as monitoring organisms. The high concentrations of cadmium found in molluscs from discharge areas do apparently not affect the organisms themselves. However, the molluscs may prove to be a danger for less resistant organisms (fish, birds) if they feed exclusively on contaminated molluscs. Aquatic organisms differ widely in their sensitivity to cadmium. In some forms of marine and fresh water phytoplankton, growth is reduced at concentrations of 2-10 .ug Cd/l. In fresh water, cladocerans and salmonids tend to be the most sensitive groups with chronic toxicities in soft water in the range 0.4 to 1.0 .ug Cd/l. As calcium ions seem to protect aquatic organisms against cadmium toxicity, their resistance is markedly raised in hard water. In sea water, planktonic crustaceans prove to be the most sensitive group to cadmium intoxication (lowest recorded chronic value 6.4 .ug Cd/l). Toxicity of cadmium is negatively correlated to sa1inity. Thus, the toxicity of cadmium to marine organisms is significantly increased at low salinities. The following conclusion may be drawn that, due to the rather low toxicity to most marine life, cadmium probably presents no problems in Danish marine areas. However, in higher long-lived marine animals from other sea areas, contaminated with cadmium, adverse effects may be found, especially in liver and kidneys. Organisms in fresh water are much more sensitive to cadmium pollution than are marine organisms, and biological effects of cadmium are mani- fested at markedly low concentrations, especially in soft water.

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