The bioavailability of potentially toxic metals in aquatic systems is frequently related to the dissolved free metal ion(M~(2+))concentration.However,typical methods used to determine M~(2+)are labor intensive or require sophisticated equipment.We developed an inexpensive,in situ sampling device-the "gellyfish"-that simplifies Cu~(2+)determinations in seawater.The gellyfish is a thin disk of polyacrylamide gel embedded with iminodiacetate(Id)groups bound to immobile beads.The sampler operates on the principle that the immobilized Id groups equilibrate with the Cu~(2+)concentration of the surrounding solution.Cu is then back-extracted into a known volume of 10 HMO_3 and measured by inductively coupled plasma mass spectrometry(ICP-MS).In laboratory tests,we varied Cu~(2+)concentrations between 10~(-12)and 10~(-8)M and salinity between 5 and 35 ppt.Id-bound Cu(Culd_mearsured)did not respond to changes in total Cu.However,Culd_measured does increase in a predictable manner with increasing Cu~(2+),and prototype gellyfish precision(average coefficient of variation= 10)is sufficient to resolve small differences in Cu~(2+)(+-30).Modeled Cu uptake,based on thermodynamic equilibrium speciation of Id within gellyfish,is a good predictor of Culd_measured(r~2=0.96 and n= 45).
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Exposure,Epidemiology,and Risk Program,Department of Environmental Health,Harvard School of Public Health,665 Huntington Avenue,Boston,Massachusetts 02115;
