OLD PAYSON DRY CLEANERS
PAYSON, GILA COUNTY, ARIZONA
Studies have shown that inhalation exposure from residential uses of VOC contaminated water may equal or exceed those of ingestion. According to the EPA, the greatest risk posed by halogenated hydrocarbons, such as PCE, from indoor water activities occurs in the shower, when the volatilization from water to air is at a maximum [Wiley, 1991]. Furthermore, bathroom activities account for nearly two-thirds of the total daily per capita domestic water usage [Andelman, et. al, 1990]. A well studied model shows that the inhalation dose from a shower exposure for a 70 kg man taking a fifteen minute shower at a efflux rate of 10 L/minute once a day is equivalent to a two liter ingestion exposure [McKone and Knezovich, 1991]. The model applies standard residential exposure assumptions.
Inhalation intakes were calculated based on this McKone and Knezovich model. The daily exposure dose for a 16 kg child is 0.001 mg/kg/day and 0.00046 mg/kg/day for a 70 kg adult. Acute inhalational minimal risk levels (MRL) is 0.213 mg/kg/day for a 16 kg child taking a 15 minute shower, and 0.097 for a 70 kg adult. Chronic MRL is 0.042 mg/kg/day for a 16 kg child exposed to PCE in the shower, and 0.02 mg/kg/day for an adult. The MRL's account for an uncertainty factor of 100 (10 for the use of a LOAEL, and 10 for cross species extrapolation)[ATSDR Toxicological Profile for PCE, Sept. 1997]. The hazard quotient, an index reflective of relative risk from a given pathway, is calculated to be 0.005 for acute exposure and 0.023 for chronic inhalational exposure. Since the risk is found to be less than one, it is considered minimal.
As stated previously, Andelman, et. al. report that bathroom activities account for two-thirds of residential usage. Drinking water is the other main residential use. Therefore, the remaining domestic uses such as cooking, laundry, and dishwashers all combined contribute much less than one third of total water usage and are individually insignificant factors in exposure.
Ingestion is not a potential pathway of exposure since trailer park residents are being provided bottled drinking water.
The dermal dose for a 70 kg adult with an estimated body surface area of 20,000 cm2 is calculated to be 0.000055 mg/kg per fifteen minute shower. For a 16 kg child, with an estimated body surface area of 9,000 cm2, we estimate an absorption of approximately 0.00011 mg/kg PCE for each fifteen minute shower. No animal or human studies were available in the toxicological profiles with known systemic toxic effects from specific dermal doses. Therefore, no reference dose exists. The hazard quotient, 0.022 for a child, and 0.011 for an adult, is extrapolated from the oral reference dose assuming a 10% absorption efficiency for organics [PEA, Cal EPA,1994].
The same subpopulations are subjected to both dermal and inhalation exposure, and thus the
combined exposure must also be considered. The hazard index is reflective of multiple pathway
exposure for the trailer park residents, and is calculated by adding the individual hazard quotients
from each of the dermal and inhalation exposures. The hazard indexes indicate no risk, as they
are below one for both acute (HI=0.016) and chronic exposure (HI=0.034).
The hazard indexes for children are 0.027 for acute and 0.046 for chronic exposure, again less than one, so there is no cumulative risk posed at the concentration of PCE present in the trailer park well. Sensitive subpopulations tend to be children whose systems are still developing, and elderly people who may be immune compromised, but at these calculated daily doses, even the most sensitive populations are unlikely to be affected. There are no known, observed health effects from exposure to PCE at the daily doses that the Payson trailer park residents are being exposed to from their private well water.