The East Bay Diesel Exposure Project: a biomonitoring study of parents and their children in heavily impacted communities

Diesel exhaust (DE) poses significant health risks, including asthma and lung cancer, particularly impacting low-income and minority communities in California that already face multiple environmental and socioeconomic stressors. While California regulations have reduced overall DE emissions, some areas, like West Oakland, still experience high pollution levels due to localized sources such as ports, rail yards, and highways. The California Environmental Contaminant Biomonitoring Program (CECBP) identified 1-nitropyrene (1-NP) metabolites, specifically 6-hydroxy-1-nitropyrene (6-OHNP) and 8-hydroxy-1-nitropyrene (8-OHNP), as viable biomarkers for DE exposure due to their presence in DE and ease of urine sample collection. Previous studies have shown positive associations between urinary 1-NP metabolites and airborne 1-NP, with higher levels observed in areas with greater diesel traffic. This study, the East Bay Diesel Exposure Project (EBDEP), aimed to evaluate DE exposure in families with young children by combining 1-NP biomonitoring with household dust and indoor air measurements to provide a comprehensive assessment of exposure and inform mitigation strategies.

The literature review extensively cites prior research demonstrating the disproportionate impact of diesel exhaust on vulnerable communities in California, linking DE exposure to various health problems like asthma, cancer, and cardiovascular disease. The selection of 1-nitropyrene (1-NP) and its metabolites as biomarkers is justified by existing studies that establish its preferential formation during high-temperature combustion in diesel engines and its abundance in airborne particulate matter from DE. Previous studies are referenced that highlight the positive correlations between urinary 1-NP metabolites and airborne 1-NP levels, as well as studies showing higher levels of 1-NP metabolites in areas with elevated diesel vehicle traffic. A pilot study in the Salinas Valley and Oakland is mentioned as informing the design of EBDEP, highlighting the need for a more comprehensive, family-based investigation.

The EBDEP recruited 40 parent-child pairs (n=80) from Oakland, Richmond, and nearby communities in the San Francisco East Bay, targeting areas with varying levels of estimated DE exposure based on the CalEnviroScreen 3.0 diesel PM indicator. Recruitment occurred through community organizations, health clinics, and other public venues. Each family participated in two sampling rounds, four months apart. In the first round, study staff collected initial questionnaires, GPS data, time-activity diaries, and household dust samples. For 25 families, a single spot urine sample was collected on day four; for the remaining 15 families, daily urine samples were collected for four consecutive days. The second round repeated the questionnaires and urine collections, but not the dust sampling. Indoor air samples for 1-NP were also collected using Aerosol Black Carbon Detectors (ABCD) during both rounds. The exposure questionnaires gathered demographic information, potential exposure determinants (occupation, location, vehicle use, etc.), and smoking history. The home walkthrough collected additional environmental information on heating systems, stove fans, etc. Urine samples were analyzed for 6-OHNP and 8-OHNP using high-performance liquid chromatography with tandem mass spectrometry (HPLC-MS/MS). Dust and air samples were analyzed for 1-NP using similar methods. Data analysis involved calculating summary statistics, correlation coefficients (with weights inversely proportional to the number of measurements), and the use of random-effects and mixed models to analyze log-transformed metabolite data, accounting for multiple samples from participants and seasonal effects. Within- and between-subject variability was assessed using the intraclass correlation coefficient (ICC) for the participants who provided daily samples. The relationship between CalEnviroScreen 3.0 diesel PM scores and 1-NP levels (dust, air, and urinary metabolites) was evaluated using t-tests and mixed models.

1-NP metabolites were detected in almost all (96.6%) urine samples. Parents had significantly higher 6-OHNP concentrations than their children (p=0.005). 8-OHNP concentrations were also higher in parents, but not significantly. Metabolite levels were generally higher during the fall and winter months. Within-subject variability was considerably higher than between-subject variability (~60% vs. ~40% of total variance), indicating high short-term fluctuations. Household dust 1-NP detection frequency was 97%, and indoor air was 74%. 1-NP levels were moderately correlated in dust and indoor air. Parents in the highest income bracket (>$75,000) had significantly higher metabolite concentrations than those in lower income brackets. No associations were found between metabolite levels and race/ethnicity. Higher CalEnviroScreen diesel PM scores were associated with elevated 1-NP concentrations in indoor air and house dust, but not in urinary 1-NP metabolites.

The high detection frequency of 1-NP metabolites indicates widespread DE exposure among the study population. The higher levels of 6-OHNP in parents compared to children warrant further investigation into potential explanations. The seasonal variation aligns with expectations, given increased air pollution during fall and winter due to temperature inversions. The lack of significant associations between metabolite levels and race/ethnicity, despite targeting disproportionately impacted communities, might reflect limitations in capturing the complexity of individual exposure patterns. The income-related differences highlight the importance of socioeconomic factors in influencing exposure. The higher within-subject variability emphasizes the need for longer-term sampling to accurately characterize individual exposures. The study's findings highlight the value of combining biomonitoring with air and dust monitoring to refine our understanding of hyperlocal DE exposures and the spatial variability of pollution.

The EBDEP provides valuable insights into DE exposure in families residing in heavily impacted communities. The study demonstrates the utility of biomonitoring in assessing hyperlocal pollution impacts. The high within-subject variability underscores the need for longer-term sampling strategies in future studies. Further research should investigate factors influencing exposure patterns, such as proximity to specific sources and meteorological events, to refine our understanding and support the development of effective mitigation strategies.

The relatively small sample size limited the power to detect associations with some demographic factors and might have influenced the results. The study design did not fully capture the intended seasonal comparison due to recruitment challenges. The short-term sampling might not fully capture longer-term exposure patterns. The reliance on self-reported data for certain exposures introduces potential recall bias.