Health Hazard Assessment for Native Americans Exposed to the Herbicide Fluridone via the Ingestion of Tules at Clear Lake, California, USA

ABSTRACT

This study addresses concerns expressed by Native Americans regarding exposure via the consumption of aquatic vegetation to the herbicide fluridone (active ingredient) used by the California Department of Food and Agriculture (CDFA) Hydrilla Eradication Program in Clear Lake, California. In 2005, the Department monitored lakeshore vegetation, water, and sediment at four locations, before and after seasonal applications of fluridone. Subchronic and chronic exposures were evaluated, and hazard quotients calculated for a worst-case exposure (WCE) scenario. Ingestion rates and other exposure factors were developed in public meetings with tribal members. Environmental sampling found fluridone present at extremely low levels in tule vegetation, water, and sediment. Exposures were four times greater in subchronic timeframes than chronic timeframes; however, hazards were less due to the 25-fold larger reference dose (RfD) used for subchronic calculations: RfD_(subchronic) = 2.0 mg/kg-day, RfD_(chronic) = 0.08 mg/kg-day. Conservative, child, total daily ingestion (TDI) doses were calculated to be 8.3 × 10⁻⁵ mg/kg-day (subchronic) and 2.1 × 10⁻⁵ mg/kg-day (chronic). Hazard quotients (HQ) for subchronic and chronic exposures were on the order of 10⁻⁵ and 10⁻⁴, respectively, indicating that at current application regimes, there is little to no hazard of adverse effects from fluridone exposure via ingesting Clear Lake tules.

Key Words:

• Native American
• exposure
• hazard
• fluridone
• tules

Notes

*Pre-treatment,

**Post-treatment.

^a IR = Ingestion Rate.

^b ADD = Average Daily Dose.

^c RfD = Reference Dose.

^d HQ = Hazard Quotient.

^e Sed. = Sediment.