RESUMO
Hair relaxers have been suggested as a source of exposure to parabens and phthalates. However, dermally absorbed doses of these chemicals resulting from consumer use of hair relaxers have yet to be quantified, and results from epidemiological studies have consistently demonstrated that there is no increased risk for hormone-sensitive, reproductive cancers associated with use of hair relaxers among Black women. Therefore, dermal absorption of parabens and phthalates associated with hair relaxer use for several commercially available hair relaxer kits was modeled using IH SkinPerm™. The chemicals detected in the hair relaxer kits included methylparaben (MP), ethylparaben (EP), butylparaben (BP), diethyl phthalate (DEP), bis(2-ethylhexyl) phthalate (DEHP), and the phthalate substitute bis(2-ethylhexyl) adipate (DEHA). The daily absorbed dose ranges (mg/kg/day), standardized over a year of product use, were as follows: 8.64 × 10-5-0.00116 MP, 2.30 × 10-8-3.07 × 10-6 EP, 3.24 × 10-8-4.33 × 10-6 BP, 8.65 × 10-9-1.15 × 10-6 DEP, and 8.94 × 10-7-0.000119 DEHP for Kit #1; 8.44 × 10-5-0.00113 MP and 7.91 × 10-5-0.00106 DEP for Kit #2; and 2.49 × 10-6-3.33 × 10-5 MP, 1.52 × 10-8-2.03 × 10-6 EP, 3.29 × 10-9-4.39 × 10-7 DEP, and 3.11 × 10-6-4.14 × 10-5 DEHA for Kit #3. These absorbed doses were well below applicable health-based guidance values, indicating consumer exposure from product use is not expected to pose a health risk. These results provide valuable information for health risk evaluations for hair relaxer use.
RESUMO
In aquatic ecosystems, plastic litter is a substrate for biofilms. Biofilms on plastic and natural surfaces share similar composition and activity, with some differences due to factors such as porosity. In freshwaters, most studies have examined biofilms on benthic substrates, while little research has compared the activity and composition of biofilms on buoyant plastic and natural surfaces. Additionally, the influence of substrate size and successional stage on biofilm composition has not been commonly assessed. We incubated three plastics of distinct textures that are buoyant in rivers, low-density polyethylene (rigid; 1.7 mm thick), low-density polyethylene film (flexible; 0.0254 mm thick), and foamed polystyrene (brittle; 6.5 mm thick), as well as wood substrates (untreated oak veneer; 0.6 mm thick) in the Chicago River. Each material was incubated at three sizes (1, 7.5, and 15 cm2 ). Substrates were incubated at 2-10 cm depths and removed weekly for 6 weeks. On each substrate we measured chlorophyll concentration, biofilm biomass, respiration, and flux of nitrogen gas. We sequenced 16S and 23S rRNA genes at Weeks 1, 3, and 6 to capture biofilm community composition across successional stages. Chlorophyll, biomass, and N2 flux were similar across substrates, but respiration was greater on wood than plastics. Bacterial and algal richness and diversity were highest on foam and wood compared to polyethylene substrates. Bacterial biofilm community composition was distinct between wood and plastic substrates, while the algal community was distinct on wood and foam, which were different from each other and polyethylene substrates. These results indicate that polymer properties influence biofilm alpha and beta diversity, which may affect transport and distribution of plastic pollution and associated microbes, as well as biogeochemical processes in urban rivers. This study provides valuable insights into the effects of substrate on biofilm characteristics, and the ecological impacts of plastic pollution on urban rivers. PRACTITIONER POINTS: Plastic physical and chemical properties act as forces of selection for biofilm. Biofilm activity was similar among three different types of plastic. Community composition between plastic and wood was different.