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Dermal Irritancy Assessment of Water Contaminating Pesticides and Biological Toxins using Two- and Three-dimensional Human Skin Models
Citation:
Hughes, M. AND D. Ross. Dermal Irritancy Assessment of Water Contaminating Pesticides and Biological Toxins using Two- and Three-dimensional Human Skin Models. SOT, Salt Lake City, UT, March 10 - 14, 2024. https://doi.org/10.23645/epacomptox.25400176
Impact/Purpose:
Poster presented to the Society of Toxicology (SOT) 63rd Annual Meeting and ToxExpo March 2024
Description:
The contamination of public water systems with pesticides and biological toxins is a common occurrence. As people may swim and bathe in contaminated waters, the dermal exposure to these contaminants may result in irritation of the skin. The objective of this study was to assess the in vitro dermal irritancy potential of selected pesticides and biological toxins listed on EPA’s Contaminant Candidate List. Chemicals and toxins on this list are known or anticipated to occur in public water systems; future regulation under the Safe Drinking Water Act may be required. Two- and three-dimensional (2D and 3D, respectively) models were used to assess dermal irritancy. The 2D model consisted of normal human keratinocytes plated in 96-well plates at 10000 cells/well. The 3D model was EpiDermTM, which is derived from normal human keratinocytes that are specifically cultured to form a multi-layered differentiated human epidermal model. Chemicals included oxyfluorfen (OXY), permethrin (PER), profenofos (PRO), dimethipin (DIM), tribufos (TRI), and 1,2,3,4,5,6-hexachlorocylo-hexane (BHC). Toxins included cylindrospermopsin (CYL) and microcystin (MC) -LR, -RR and -LA. The effect of a mixture (1:1) of CYL and MC-LR was also assessed. Doses began at 10-fold over the reference concentration, then 50-, 100-, 500-, 1000-, and 5000-fold greater. Negative (media with contaminant vehicle) and positive (5% sodium dodecyl sulfate) controls were included. The cells in the 2D model were exposed to contaminant for either 1 or 24 hr. After the exposure, media containing contaminant was removed, fresh media was added, and then viability was assessed using the MTT assay. In the 3D model, contaminant was applied to the epidermal surface, with exposure for either 1 or 24 hr. After exposure, media with contaminant was removed, and fresh media was added. Twenty-four hr. later, media was refreshed again. The following day, viability was assessed using the MTT assay. Results were determined relative to negative control. For the 2D model, significant effects on viability were observed at 1 hr for MC-LR (increase, 2 mg/L), OXY (decrease, 10 mg/L) and TRI (decrease, 60 mg/L); at 24 hr., for CYL (increase, 0.2 mg/L; decrease, 4 mg/L), MC-LR (decrease, 4 mg/L), DIM (increase, 0.28, 2.8-14 mg/L), OXY (decrease, 0.1 and 10 mg/L), PER (decrease, 60-300 mg/L) and TRI (decrease 30 and 60 mg/L). For the 3D model, significant effects on viability were observed at 1 hr, for CYL (increase, 0.4 mg/L), MC-LA (decrease, 0.2 mg/L); at 24 hr, BHC (decrease, 30 and 60 mg/L), MC-RR (decrease, 0.02 mg/L) and OXY (increase, 1 mg/L; decrease, 4 and 10 mg/L). PRO and the mixture of CYL and MC-LR had no effect on either model. The 2D model appeared to be more sensitive to the contaminants, particularly after 24 hr. exposure. The 3D model may be less sensitive because it contains a stratum corneum, unlike the keratinocytes. Only CYL and OXY had effects on viability in both models. For CYL, an increase was observed in the 2D model and increases and decreases in the 3D model. For OXY, increases and decreases were observed in the 2D model and decreases in the 3D model. The greatest decrease in viability in the 2D model was MC-LA at 1 hr (16% decrease) and OXY at 24 hr. (26% decrease). For the 3D model, the greatest decrease in viability was caused by TRI at 1 hr. (23% decrease) and MC-LR at 24 hr. (32% decrease). The Organization for Economic and Cooperation Development’s Test Guideline (439) on skin irritation recommends contaminants that decrease viability in the 3D model following 1 hr. exposure by 50% be considered dermal irritants. Under the conditions tested here, it appears none of the chemicals and biological toxins assessed in both models can be considered dermal irritants. This abstract does not represent US EPA policy.
URLs/Downloads:
DOI: Dermal Irritancy Assessment of Water Contaminating Pesticides and Biological Toxins using Two- and Three-dimensional Human Skin Models
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