Sensitizing potential of chromated copper arsenate in local lymph node assays differs with the solvent used

We used the local lymph node assay to evaluate the abilities of chromated copper arsenate (CCA), a commonly used wood preservative, and its components to cause sensitizing reactions after their dilution in acetone-olive oil (AOO) and dimethyl sulfoxide (DMSO). After CBA/J mice were treated topically with 0.3 to 10% CCA, 0.3-3% chromium oxide, 0.3-3% arsenic oxide, or 0.3-3% copper oxide, their auricular lymph nodes (LN) were weighed and used in lymphocyte proliferation assays. In addition, total levels of chromium and arsenic in blood samples were measured. In all groups treated with CCA in AOO or DMSO, all parameters, including LN weight and lymphocyte proliferation, increased in a dose-dependent manner. The stimulation index (SI; the mean [3H]-TdR incorporation of the treatment group divided by that of the control group) showed a positive response (SI > 3) in all treatment groups; the EC3 values (estimated concentration to yield SI of 3) of CCA in AOO and DMSO were 1.86% and < 0.3%, respectively. In addition, we confirmed that the three components of CCA--chromium oxide, arsenic oxide and copper oxide--each individually exerted sensitizing ability. Mice treated with arsenic oxide in AOO or DMSO yielded nearly equal positive responses; however, the LLNA responses in mice treated with chromium oxide and copper oxide was much higher in the DMSO groups than in the AOO groups. The total chromium level in blood was higher in DMSO groups than AOO groups, whereas arsenic levels were comparable between the DMSO and AOO groups. Our findings suggest that CCA has sensitizing activity and that the type of solvent used can influence the results of sensitization assays evaluating metals.