POPs - schwer abbaubare Chemikalien

POPs, persistent organic pollutants, are slowly degradable, bio-accumulative and toxic substances. Most of them are semivolatile and lipophilic. In the atmosphere they sorb to aerosol particles, and upon deposition to soil or water surfaces they may return through volatilisation, enabling them to undergo sequential cycles of emission, atmospheric transport and deposition. These patterns of transport and distribution as well as the long-range transport potential differ significantly from those of conventional air pollutants, which undergo only one such cycle. The capability to travel long distances by several hops is called the grasshopper effect. According to a key hypothesis of environmental chemistry the accumulation of persistent and bio-accumulative pollutants in polar regions, far from the areas of usage, is due to the combination of the grasshopper effect and enhanced condensation in cold areas. Lipophilicity is a prerequisite for bio-accumulation and influences the partitioning among environmental media (multicompartment compounds). As POPs are typically halogenated compounds, chemical degradation in the atmosphere is in most cases slower than of other air pollutants, but faster than in the other environmental compartments, where persistence coincides with residence times of months. The long-range transport potential and persistence are crucial for chemical hazard assessment. These characteristics result from the combined action of physico-chemical properties and environmental conditions variable in time and space. Hence, they vary in time and space