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The primary source of formaldehyde indoors is composite wood products manufactured <br />with urea -formaldehyde resins, such as plywood, medium density fiberboard, and <br />particleboard. These materials are commonly used in building construction for flooring, <br />cabinetry, baseboards, window shades, interior doors, and window and door trims. <br />In January 2009, the California Air Resources Board (CARE) adopted an airborne toxics <br />control measure (ATCM) to reduce formaldehyde emissions from composite wood <br />products, including hardwood plywood, particleboard, medium density fiberboard, and also <br />furniture and other finished products made with these wood products (California Air <br />Resources Board 2009). While this formaldehyde ATCM has resulted in reduced emissions <br />from composite wood products sold in California, they do not preclude that homes built <br />with composite wood products meeting the CARB ATCM will have indoor formaldehyde <br />concentrations below cancer and non -cancer exposure guidelines. <br />A follow up study to the California New Home Study (CNHS) was conducted in 2016-2018 <br />(Singer et. al., 2019), and found that the median indoor formaldehyde in new homes built <br />after 2009 with CARB Phase 2 Formaldehyde ATCM materials had lower indoor <br />formaldehyde concentrations, with a median indoor concentrations of 22.4 µg/m3 (18.2 ppb) <br />as compared to a median of 36 µg/m3 found in the 2007 CNHS. Unlike in the CNHS study <br />where formaldehyde concentrations were measured with pumped DNPH samplers, the <br />formaldehyde concentrations in the HENGH study were measured with passive samplers, <br />which were estimated to under -measure the true indoor formaldehyde concentrations by <br />approximately 7.5%. Applying this correction to the HENGH indoor formaldehyde <br />concentrations results in a median indoor concentration of 24.1 µg/m3, which is 33% lower <br />than the 36 µg/m3 found in the 2007 CNHS. <br />Thus, while new homes built after the 2009 CARB formaldehyde ATCM have a 33% lower <br />median indoor formaldehyde concentration and cancer risk, the median lifetime cancer risk <br />is still 120 per million for homes built with CARB compliant composite wood products. <br />This median lifetime cancer risk is more than 12 times the OEHHA 10 in a million cancer <br />risk threshold (OEHHA, 2017a). <br />3of19 <br />