To assess the fate of current-use pesticides, it is important to understand their bioaccumulation and biotransformation by aquatic biota. We examined the dietary accumulation and enantioselective biotransformation of the chiral current-use pesticide fipronil, along with a mixture of selected chiral [alpha-hexachlorocyclohexane (alpha-HCH), heptachlor epoxide (HEPX), polychlorinated biphenyls (PCBs) 84, 132, 174, o,p'-DDT, and o,p'-DDD] and nonchiral (p,p'-DDT, p,p'-DDD) organochlorine compounds in juvenile rainbow trout (Oncorhynchus mykiss). Fish rapidly accumulated all compounds, as measured in the carcass (whole body minus liver and GI tract) during the 32 d uptake phase, which was followed by varying elimination rates of the chemicals (half-lives (t1/2s) ranging from 0.6 d for fipronil to 77.0 d for PCB 174) during the 96 d depuration period. No biotransformation was observed for alpha-HCH, HEPX, PCB 174, o,p'-DDT, or o,p'-DDD based on consistent enantiomeric fractions (EFs) in the fish and their t1/2s falling on a log K(ow)--log t1/2 relationship established for recalcitrant contaminants in fish. p,p'-DDT and PCBs 84 and 132 were biotransformed based on the former's t1/2 position below the log K(ow)--log t1/2 relationship, and the PCBs change in EF. Fipronil was rapidly biotransformed, based on a change in EF, a t1/2 that fell below the log K(ow)--log t1//2 relationship, which accounted for 88% of its elimination, and the rapid formation of fipronil sulfone, a known metabolite. Fipronil sulfone was found to persist longer (t1/2 approximately 2 d) than its parent compound fipronil (t1/2 approximately 0.6 d) and needs to be considered in fate studies of fipronil. This research demonstrates the utilities of the log K(ow)--log t1/2 relationship as a mechanistic tool for quantifying biotransformation and of chiral analysis to measure biotransformation in fish.

The susceptibility of isolated cell walls to solubilization by polygalacturonase and the effect of pectinesterase on the solubilization were examined. The two polygalacturonases in ripe tomatoes were purified to remove pectinesterase. Both polygalacturonases solubilized uronic acid from pectinesterase‐free tomato cell walls most rapidly at about pH 3.5, well below p H 4.5, the pH optimum for their hydrolysis of pectic acid. At p H 3.5, very low levels of pectinesterase increased cell wall solubilization by the polygalacturonases seueralfold, whereas high concentrations of pectinesterase completely inhibited solubilization. A t pH 5, pectinesterase also increased cell wall solubilization, but higher concentrations were required than at pH 3.5 and high levels were not inhibitory. The materials solubilized at pH 3.5 were galacturonan with a molecular weight of about 110,000 and two fractions of much higher molecular weights consisting primarily of neutral sugars. Galactose accounted for about two‐thirds of the monosaccharides in the neutral polysaccharides.

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