The In Vitro Percutaneous Absorption of Radiolabelled Biocide in a Single Solvent-Based Paint Formulation Through Human Skin

has considered including 50% of the material associated with the stratum corneum in the dermal delivery (skin and receptor fluid) value. Clearly for test items, such as biocidal paints, that are not efficiently removed from the skin during the washing procedure, this will have a significant impact on the resultant safety assessment. In this study, we have examined the dermal penetration of a biocide (mwt 349.5, LogP ow 5.85, pH 7) used in antifouling paints marketed by International Paint Ltd. was 0.36% (skin wash: 0.23%, tissue swabs: 0.13%). At 24 h post dose, the donor chamber contained 4.96%, so total dislodgeable dose was 5.36%. The stratum corneum contained 95.34% (tapes 1-5, 6-10, 11-15, 16-20 and 21-25 contained 94.69%, 0.50%, 0.04%, 0.04% and 0.06%, respectively). This is shown graphically in Figure 1. Total unabsorbed dose was 100.70%. The absorbed dose and dermal delivery were 0.78% (receptor fluid: 0.77%, receptor rinse: 0.02%) and 0.94% (absorbed dose + exposed skin: 0.15%), respectively. The lag time was ca 4 h. Steady state flux (0.25 µg equiv./cm 2 /h) was achieved from 10-24 h post dose. The absorption profile is presented in Figure 2. The data are summarised as µg equiv./cm 2 in Table 1 and the absorption profiles presented in Figure 3 and Figure 4. The highest rate of absorption (0.30 µg equiv./cm 2 /h) was evident in the 2 h following the 8 h washing procedure. Adding 50% of the total stratum corneum (47.67%) to dermal delivery, results in an unrealistic revised value for risk assessment of 48.61% since the rate of absorption into the epidermis/dermis and receptor fluid is so low. Taking a highly conservative approach, material in tape strips 16-25 or 11-25 may be considered as potentially absorbable, due to their closer proximity to the epidermis, resulting in revised values of 1.04% or 1.08%, respectively for dermal delivery. However, since the biocide remained within the stratum corneum after the 24 h study period, this suggests that even the biocide in the lower layers would be unlikely to pass through to the viable tissue. Operators using such antifouling products are extremely unlikely to leave paint on their skin for 24 h. Therefore, it is unrealistic to add the stratum corneum biocidal loading to the dermal delivery value.