Disposition and taurine conjugation of 2,4-dichlorophenoxyacetic acid, 2,4,5-trichlorophenoxyacetic acid, bis(4-chlorophenyl)acetic acid, and phenylacetic acid in the spiny lobster, Panulirus argus
The disposition of 2,4-dichlorophenoxyacetic acid (2,4-D) 2,4,5-trichlorophenoxyacetic acid (2,4,5-T), bis(4-chlorophenyl)acetic acid (DDA), and phenylacetic acid (PAA) were studied in a marine crustacean, the spiny lobster, Panulirus argus, after injecting doses of the respective 14C-labeled acids (10 mg/kg + 10-20 μCi/kg) into the pericardial sinus. The tissue distribution of the 14C was determined at intervals of 0.5 hr to 3 wk, depending on the acid. Hemolymph, urine, and hepatopancreas (HP) were analyzed for the presence of metabolites. The major excretory organs, green gland (equivalent to kidney) and HP (equivalent to liver) concentrated each acid from hemolymph. At 6 hr after the dose, the green gland:hemolymph concentration ratios were similar for each acid (about 10) whereas the HP/hemolymph concentration ratios varied. The 6-hr HP/hemolymph concentration ratios were 80 for PAA, 10 for DDA, 1.8 for 2,4-D, and 1.2 for 2,4,5-T. The portion of each acid that accumulated into green gland was excreted in 'urine' as parent acid, and for those acids that did not accumulate preferentially into HP (2,4-D and 2,4,5-T), urinary excretion was the major route of elimination. The portion of 2,4-D, 2,4,5-T, DDA, or PAA that accumulated into HP was metabolized to the respective taurine conjugate and excreted very slowly, apparently via the digestive tract. Uptake and metabolism in HP was a major pathway for PAA and DDA. The slow excretion from HP appeared to be due to enterohepatic circulation. Examination of the 24-hr total body burdens of each acid (12% of dose for 2,4-D, 28% of dose for 2,4,5-T, 58% of dose for PAA, and 76% of dose for DDA) suggested that excretion of the unchanged acid in urine was a more efficient method of elimination than conjugation in HP. Thus, in the lobster, conjugation of an exogenous carboxylic acid (PAA, DDA, 2,4-D, 2,4,5-T) with taurine did not facilitate excretion.