Organic Micropollutants in Dutch Coastal Waters

During six cruises in the period August 1983 - July 1984, water samples were collected at nine locations in the Southern North Sea in order to assess the level of contamination with some classes of organic micropollutants for which presently little information is available. Thirty-one individual compounds (chlorobenzenes, chloronitrobenzenes, nitrotoluenes, halogenated aliphatic hydrocarbons, alkylbenzenes, polycyclic aromatic hydrocarbons) were measured. Concentration levels were found to be in the lower ng/1 (ppt) range: frequently close to the blank levels or below the limits of detection. Statistical data analysis revealed that both spatial and temporal variations were significant for nearly all parameters, and that nearly all parameters were significantly correlated with each other as well as with the salinity. Using principal components analysis, variations in the contamination with trace organics can be semi-quantitatively described with one component only. The highest concentrations were observed in the coastal waters north of the Rhine/Meuse estuary. Concentrations gradually decrease in northerly direction and sharply fall in seaward direction. It is proposed that the observed concentration levels are the result of two physical phenomena: (i) mixing of relatively uncontaminated water from the Atlantic Ocean with polluted water from the Rhine/Meuse estuary, and (ii) air-sea exchange by volatilization-, dry- and wet deposition processes.