Evaluation of exposures to diesel particulate matter utilizing personal air monitoring and urinary biomarkers among pedestrian commuters who cross the U.S.-Mexico border at San Ysidro, CA

Walk-in-line pedestrians crossing the U.S.-Mexico border northbound at the San Ysidro, CA Port of Entry may be at an increased risk from traffic-related pollution including elevated diesel particulate matter (DPM) exposure. DPM exposure has been associated with numerous adverse health effects, including respiratory problems and lung cancer. Pedestrian crossers wait in line for extended periods and stand within 10 feet of highly concentrated traffic, including diesel buses. Understanding the magnitude of traffic-related exposures is important for this vulnerable population. It is hypothesized that subjects who reside in Tijuana, B.C. and cross the border as a pedestrian will experience higher exposure to traffic-related pollutants than those who live and work in South San Diego, CA and do not cross the border. Ninety-one participants were enrolled for this study; 79% subjects and 21% controls. Questionnaires and urine samples were collected from all participants. Of the subjects, 56 personal 24-hour 1-NP (a marker for diesel); 17 at-home indoor and outdoor 24-hour 1-NP; and 35 days of 1-NP, CO, PM2.5 and ultrafine (<0.1um) area monitoring at the border were collected. Of the controls 16 personal 24-hour 1-NP, and 4 at-home indoor and outdoor 24-hour 1-NP were collected. Studies indicate 1-NP to be concentrated in ultrafine particulate matter (UFP), which is of significance health concern considering UFP show much higher deposition to the pulmonary alveoli than fine particulate matter (PM2.5). Median ultrafine concentrations at the border were extremely high with a median of 37,336 #/cm³(range 279-230,523 #/cm3). Further analysis is currently underway with an addition of questionnaires elucidating the relationship between traffic pollutant, specifically DPM exposure and risk factors such as gender, age, season, frequency, and wait time at the border. Our results to date have indicated that measures to reduce wait times would significantly reduce traffic pollutant exposures in this vulnerable population.