Levels and long-term trends of polychlorinated biphenyls and DDTs in mussels collected from the middle adriatic coastal waters.

It is well documented that synthetic chlorinated hydrocarbon residues are widespread through the oceanic ecosystem. The Adriatic Sea, as semienclosed body of water, is of special interest for an evaluation of the entry, extent and fate of the pollution by chlorinated hydrocarbons. An investigation of chlorinated hydrocarbons levels in mussels in the middle Adriatic coastal waters, Croatia was performed. Samples were collected between 1974 and 1990 at several stations located in the middle Adriatic coastal waters. It is very important to stress that all these samples were analyzed from a single analytical group (mostly by the same analyst), using a uniform methodology which was very successfully by intercalibrated during seven international intercalibration exercises. Mass fractions of chlorinated insecticides and polychlorinated biphenyls in mussels ranged from ND (< 0.1) to 121.3 for DDTs and from ND (< 0.5) to 478.2.10(9) wet weight for PCBs and from 21 to 18500 for DDTs and from 32 to 47200.10(9) for PCBs on extracted organic matter basis. Total DDT and PCB mass fractions do not exhibit Gaussian distribution in the investigated area and collecting period. This signifies that median and geometric means better indicate the central tendency of the investigated chlorinated hydrocarbon mass fractions than the arithmetic mean. Transforming the data to log values has the advantage of further normalizing the data, a prerequisite for the use of parametric statistics. The trend of DDTs levels is more similar to an exponential function than a linear one, so the linearization of the mass fractions data is achieved by transforming the data logarithmically.