THE RELEASE OF VOLATILE HALOCARBONS TO SEAWATER BY UNTREATED AND HEAVY-METAL EXPOSED SAMPLES OF THE BROWN SEAWEED FUCUS-VESICULOSUS

Three whole plants of the brown seaweed Fucus vesiculosus were collect ed on the western coast of Sweden and kept in 10-1 bottles with seawat er for 48 h, including light and dark periods. Two of the bottles cont ained 5 ppm mercury (as HgCl2) an 0.3 ppm tin (tributyltin fluoride), respectively. The third bottle did not contain any further additives. The concentration of volatile halocarbons was determined by capillary gas chromatography in subsamples frequently taken from each bottle. In the untreated control sample the polyhalogenated methanes, bromoform, dibromomethane, chlorodibromomethane and diiodomethane, were released in rather high amounts; up to several hundreds of ng per g dry algal tissue. The release of this group of substances, including smaller amo unts chloroiodomethane, was increased during the light periods. The mo noiodinated alkanes, iodoethane, 1-iodopropane, 1-iodobutane and 2-iod opropane, occurred at much lower concentrations in the culture medium, and the release did not show any pronounced light dependence. Exposur e of the algae to mercury(II) ions resulted in a decreased release of most of the substances measured whereas the presence of tributyltin in the seawater seemed to provoke an increased release of some halocarbo ns. Except for chloroiodomethane, no further increase in halocarbon re lease was observed after the removal of the algae from the seawater. T he results are discussed with regard to possible metabolic pathways an d sites of formation.