Exposure assessment of household mercury spills

Abstract

Elemental mercury spills in households still occur with unfortunate regularity. Devices that contain enough mercury to pose exposure concerns are common to many homes. Response to household spills differs substantially from industrial settings and improper response can increase the risk of harmful health effects. Suggested inhalation exposure levels for residential settings are much different than occupational guidelines. The characteristics of the exposed population in homes differ greatly from industrial workplace spills. Exposure assessment in the home requires the use and understanding of non-occupational guidance. The current occupational OSHA permissible exposure limit and ACGIH threshold limit value are 100 μg/m3 and 25 μg/m3, respectively. By contrast, the Agency for Toxic Substances and Disease Registry (ATSDR) Minimum Risk Level (MRL) for elemental mercury vapors is 0.2 μg/m3, well below occupational levels. The derivation of the MRL considers sensitive populations and 24 hour-a-day, seven days-a-week lifetime exposure. Occupancy criteria of 1.0 μg/m3 and 3.0 μg/m3 for residential and commercial settings have been proposed. These low levels dictate sophisticated analytical equipment or laboratory methods of analysis. Two cases illustrate how difficult it may be to assess hazards based solely on spill amount. In both cases a direct reading cold vapor atomic absorption unit was used to measure airborne mercury concentrations. Case A involved a broken thermometer spill (about 0.5 g) in a master bedroom that was cleaned using a household vacuum. Airborne concentrations throughout the home exceeded recommended exposure levels for residential settings (range of 2.5–14 μg/m3). Case B involved a broken thermostat spill (about 3.0 g) cleaned with a shop vacuum. Exposure levels were less than 1 μg/m3 throughout the home (range 0.4–0.7 μg/m3). When vacuums are used to remove mercury, quantities of mercury as small as that associated with a fever thermometer can represent an exposure hazard. The difference in exposure levels between the two cases is thought to be related to the operational differences between vacuum cleaners and the impact they had on vapor production. Unfamiliarity with the hazards posed by seemingly small amounts of mercury in the home and workplace can lead to undesirable and often costly consequences.