The uptake of monomethylmercury (mmHg) from water by larval Chaoborus
americanus was studied: When exposed to aqueous mmHg for 6 days, the p
attern of uptake was sigmoidal. The concentration of mmHg in the expos
ure water, however, was subject to demethylation and volatilization an
d therefore decreased over time. A model of passive diffusive uptake u
nderestimated the uptake constant while a bioenergetics-based uptake m
odel provided a reasonable estimate. The data suggest that uptake is n
ot merely a passive diffusive process but may be coupled with oxygen u
ptake.