Objectives: to develop and implement a follow-up protocol for Biomonitoring California study participants with elevated levels of urinary arsenic, particularly inorganic forms. Methods: We selected 20 μg/L as the level of concern for urinary inorganic arsenic; samples with total arsenic ≥20 μg/L were speciated. Participants with elevated inorganic arsenic were notified of their level and invited to participate in a telephone survey to help determine possible exposure sources. We illustrate the protocol in four Biomonitoring California studies, which collected samples from 2010–2013 in locations across the state. Results: 48 participants in the four studies had elevated urinary inorganic arsenic levels. Consumption of rice and rice-based products was the most commonly identified potential source of inorganic arsenic exposure. Conclusions: Of 48 participants with elevated inorganic arsenic, 27 would have been missed if we had used the previously published threshold of 50 µg/L total arsenic to identify urine samples for speciation. This protocol fills a gap in the clinical literature by providing a more health-protective approach to identify individuals with elevated urinary inorganic arsenic and help determine potentially significant exposure sources.

Diesel exhaust (DE) is a major traffic-related pollutant linked to adverse health outcomes, but existing methods for estimating indoor DE exposure fall short, as common surrogates like black carbon (BC), NOx, and PM2.5 are not sufficiently specific to diesel sources. 1-Nitropyrene (1-NP), a nitro-PAH preferentially formed during diesel combustion, has rarely been studied as an indoor exposure indicator. We measured 1-NP and isomeric nitro-PAHs (2-nitropyrene, 2-nitrofluoranthene) in indoor air and house dust from 40 homes in the eastern San Francisco Bay Area, CA, across two sampling events, alongside continuous indoor BC monitoring. We assessed 1-NP’s utility as a DE proxy using summary statistics, diagnostic nitro-PAH ratios, correlations with monitored pollutants, and single-predictor mixed-effects models relating 1-NP to spatial DE predictors. 1-NP was frequently detected in air (74%) and dust (97%), with median concentrations of 0.42 pg/m³ (IQR 0.32 - 0.54) and 340 pg/g (IQR 190 - 620), respectively. Air and dust 1-NP were moderately correlated (r=0.40, p = 0.02), as was BC with 1-NP (air r=0.38, dust r=0.47; p<0.01). Diagnostic ratios (2-NFl:1-NP <5) indicated dominant primary emission sources. Dust 1-NP showed numerous significant associations with spatial DE predictors, while air 1-NP showed fewer. Overall, 1-NP shows promise as a diesel-specific indoor exposure proxy integrating longer-term exposure and aligning with spatial DE predictors.

Diesel exhaust (DE) is a major traffic-related pollutant linked to adverse health outcomes, but existing methods for estimating indoor DE exposure are not validated. DE exposure indicators such as black carbon (BC), NOx, and PM_2.5 are not sufficiently specific to diesel sources. 1-Nitropyrene (1-NP), an NPAH preferentially formed during diesel combustion, has rarely been studied as an indoor exposure indicator. We measured 1-NP and isomeric NPAHs (2-nitropyrene, 2-nitrofluoranthene) in indoor air and house dust from 40 homes in the eastern San Francisco Bay Area, CA, and conducted continuous indoor BC monitoring. We assessed 1-NP’s utility as a DE exposure indicator using summary statistics, diagnostic NPAH ratios, correlations with monitored pollutants, and single-predictor mixed-effects models relating 1-NP to spatial DE predictors. 1-NP was frequently detected in air (74%) and dust (97%), with median concentrations of 0.42 pg/m³ (IQR 0.32–0.54) and 340 pg/g (IQR 190–620), respectively. Air and dust 1-NP were moderately correlated (r = 0.40, p = 0.02), as was BC with 1-NP (air r = 0.38, dust r = 0.47; p < 0.01). Diagnostic ratios (2-NFl:1-NP < 5) indicated dominant primary emission sources. Dust 1-NP showed numerous significant associations with spatial DE predictors, while air 1-NP showed fewer. Overall, 1-NP shows promise as a diesel-specific indoor exposure indicator. Future studies with larger, geographically diverse cohorts are needed to further validate this metric.