Malodors as environmental injustice: health symptoms in the aftermath of a hydrogen sulfide emergency in Carson, California, USA.

In October 2021, hydrogen sulfide (H2S), a toxic odorous gas, was measured in Carson, California at concentrations reaching 7000 parts per billion (ppb), exceeding California’s 30 ppb acute air quality standard. Thousands of residents complained of malodors and headaches. We responded to community concerns by launching a rapid survey assessing symptoms. We recruited participants through door-to-door outreach, community events, and social media. During the emergency’s first week, 75% of the 108 total respondents experienced headaches, 72% experienced dizziness, and 63% experienced difficulty sleeping. About 60% of respondents (n = 63, no response = 7) noted the odor worsening their mental health. When adjusting for age, sex, and smoking, participants <2 km from the highest H2S concentrations reported higher prevalence of agitation (PD = 0.23, 95% CI: 0.03, 0.42) and headaches (PR = 0.14, 95% CI: −0.04, 1.31) compared to participants farther away. Malodors are underprioritized in environmental justice communities, despite H2S’s effects on mental and physical health.