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The biotransformations and biomobility of monomethlarsonate and dimethylarsinate in the marine environment Nelson, John Christian


The biotransformations and the biomobility of monomethylarsonate (MMA) and dimethylarsinate (DMA) in the marine environment were investigated. The biotransformations were studied by exposing blue mussels (Mytilus edulis) to either [³H]-MMA or [³H]-DMA in seawater tanks. Metabolic products including arsenobetaine ((CH₃)₃As⁺CH₂COO⁻) were identified in both the seawater and the mussels by using chromatographic techniques. The HPLC columns were coupled to a scintillation counter which acted as the detector. Arsenobetaine was also produced in seawater tanks which did not contain mussels which indicates that arsenobetaine is biosynthesized by microscopic organisms which are naturally occurring in seawater. It is likely that the arsenobetaine found in mussels is not a metabolic product of the mussels. The biomobility ofDMA and MMA was studied by measuring the rate at which these arsenicals diffused through liposomes as models for biological membranes. (Previously studies have shown that both DMA and MMA enter cells via slow passive diffusion.) Traditional techniques employing both radiolabelled permeants and liposomal membranes showed that DMA was much more permeable to the membranes than MMA. A ¹H-NMR spectroscopic technique employing shift agents to differentiate the spectroscopic signals of the permeant on either side of the liposomal membrane, was developed to measure the rate of diffusion of molecules across membranes. This technique was applied to DMA and MMA. Permeability coefficients of(5.8 ± 1.0) x 10⁻⁸ cm s⁻¹ and (7.8 ± 2.7) x10⁻⁹ cm s⁻¹ at 24°C were measured for the neutral forms of DMA and MMA, respectively. In addition, the effects ofpH, temperature, and membrane composition on the diffusion coefficients for DMA and MMA through the liposomal membrane were investigated. It was determined that only the neutral form of these weak acids permeates across the membrane and that cholesterol decreases the rate of permeation of DMA.

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