Mercury methylation and partitioning between sediment, water and fish were
studied in river sediment spiked with mercuric chloride at levels of 1, 5 a
nd 10 ppm as Hg. Maximum methylmercury production in the sediment occurred
during the first week of incubation, with concentrations reaching 45.5 ng/g
(dry wt.). Equilibrium conditions were established 3-4 weeks after the con
tamination of the sediment with mercury. Methylmercury partitioning between
sediment and water yielded methylmercury levels of 25-154 ng/l in the fish
aquariums and 0.26 ng/l in the fish-free control after 1 week of incubatio
n. Equilibrium levels were 1.5-5.5 ng/l and 0.53 ng/l, respectively, during
the 7(th) week. Over 50% of the methylmercury in whole water were in solub
le form or associated with colloidal particulate < 1 mu m. Mercury concentr
ation in fish increased almost exponentially from 30 ppb to an average of 3
45 ppb within 3 weeks. Mercury uptake rates by fish were in the range of 10
-18 ng/g per day during the 2nd and 3rd weeks, high rates occurring in wate
r with methylmercury to total mercury ratios > 0.45. The partition coeffici
ents for total mercury and methylmercury between fish and water (Kf-w) were
5000-7000 and 10 000-22000, respectively. Large differences were observed
in methylmercury production in sediment-water incubation with fish and the
fish-free control. Equilibrium methylmercury concentrations in sediment wer
e in the range 15-32 ng/g in the aquariums containing fish and 3-4.5 ng/g i
n the fish-free control. The significance of fish in mercury methylation in
the aquariums still remains to be clarified as fish itself cannot methylat
e mercury in vivo. (C) 1999 Elsevier Science B.V. All rights reserved.