The nervous system and muscle functions may also be affected. These impacts may lead to loss of biodiversity, loss of living space and detriment to health and welfare for entire populations. Some non-degradable and slowly degradable substances can be transformed into more toxic compounds. Examples of such persistent substances are heavy metals, PCB and dioxins. Several of these substances also accumulate in the food-chains until toxic levels are reached.
Top predators are particularly vulnerable to bio-accumulation.
Combined, or synergistic effects of various environmental contaminants have produced unforeseen damage. Norway has implemented relatively strict regulations on toxic waste management, and discharges have been substantially reduced. However, there are several sites in Norway, on land as well as in the sea, where hazardous substances have been dumped or are inadequately stored. Hazardous substances threatening air, soil, water and wildlife in Norway come from other countries, as well as from national sources. Foreign-source pollution is transported to Norway by air and ocean currents.