SEDIMENT ACCUMULATION OF ORGANIC HALOGENS IN PRISTINE FOREST LAKES

Sediment accumulation of organic halogen was studied in two forest lak es, one pristine and one which received 30 m(3) of biologically purifi ed bleaching wastewater from a kraft pulp mill in 1979 equivalent to c a. 2 kg of adsorbable organic halogen (AOX). Lake sediments were dated with Pb-210, Cs-134 and Cs-137 and the annual deposition rates of org anic halogens and organic matter were calculated. Organic bound haloge n contents of the sediment aged 150 years was 180 mu g Cl g(-1) d.w. i n both lakes. The concentration of organic bound halogen at the topmos t 6 cm of the sediments (less than 20-years-old) ranged from 45 to 80 mu g Cl g(-1) d.w. This suggests that solvent extractable halogen had enriched in the older sediment layers. The deposition of extractable o rganic halogen (EOX) in the lakes in 1950's was 4 to 5 mg Cl m(-2) a(- 1). Since then, the deposition of EOX doubled in both lakes. The depos ition of organic matter increased concomitantly from 50 g to 110 g m(- 2) a(-1) in Lake Mustalampi and from 35 g m a(-1) to 62 g m(-2) a(-1) in Lake Pyylampi suggesting that the increase in the deposition of org anic halogen followed the increase in the deposition of organic matter . Of the 2 kg of organic halogen discharged into the lake, 5 % or less was detected in the sediment in tetrahydrofuran extractable form 15 y ears later.