Difference between revisions of "TCA in groundwater"

Revision as of 05:49, 14 September 2006

Introduction to Environmental risk analysis - course

Groupwork

Mikko Pohjola
Juha Villman
Anne Karvonen

James L. Byard: Hazard Assessment of 1,1,1-Trichloroethane in Groundwater

Focus: 1,1,1-Trichloroethane in Groundwater Scope: Looking at Santa Clara Valley (Silicon Valley) in California, considering primarily TCA hazard to humans. Other exposures, besides exposure to TCA in groundwater taken from wells, excluded.

Identification of Hazard

• TCA is absorbed efficiently from the gastrointestinal tract and approximately with 30% efficiency from the lungs
• Chemical is rapidly distributed to all tissues via bloodstream
• Chronic toxicity
  • Reported in several studies for no toxicity, no excess cancers, no marked oncogenic effect, no effect on mortality or body weight
  • One study reported excess of leukemias in rats exposed to TCA
• Only few weakly positive results for mutagenicity of TCA
  • These results can be explained by butylene oxide present in some commercial formulations of TCA
• No teratogenic effects in rodents exposed to TCA
• High dose of TCA can cause:
  • Narcosis
  • Mild reversible organ pathology
  • Reversible irritation of respiratory tract

Dose-Response assessment

• 15 minutes of vapor concentrations of TCA increasing from 0 to 2650 ppm
  • Mild eye irritation at 1000 - 1100 ppm
  • Throat irritation at 1900 - 2000 pm
  • Lightheadedness at 2600 ppm
  • Inability to stand at 2650 ppm

Exposure assessment

Source:

• Domestic wells
  • TCA has been widely used as an industrial degreasing solvent
  • Spills and leaking from undergound tanks have contaminated the soil
  • From soil TCA readily leches to groundwater

Routes:

• ingestion of contaminated water
• dermal contact with contaminated water
• dermal contact with vapors volatilizing from the surface of contaminated water
• inhalation of vapors volatilizing from the surface of contaminated water

Ingestion

• 2 litres of water per day per 70 kg
• Complete absorption
• 0,0286 ug/kg*day (Water containing 1 ppb TCA)

Toilet bowl

• 1 h/day
• respiration rate of 18m³/day
• 70 kg body weight
• 30 % uptake from the lungs
• 0,00032 ug/kg*day (Water containing 1 ppb TCA)

Shower

• Highest inhalation exposure due to large volume of hot water and small air volume of a shower stall
• 10 minute shower
• 50 litres of water containing 1 ppb TCA
• 0,00358 ug/kg*day
• Additional dermal vapor absortion is 1 % of the inhalation dose
• 0,0072 ug/kg*day

Bath

• 100 litres of water at 50 celcius for 20 minutes
• Total inhalation is 0,00179 ug/kg*day(Water containing 1 ppb TCA)
• Dermal absorption from the vapor is 1 %
• Dermal absorption from the bath water is 0,0457 ug/kg*day
• Total dose from bath (inhale, water and vapor) is 0,0475 ug/kg*day

Total dose

• Worst case bathroom exposure: 1 bath per day + staying bathroom for 1 hour + ingestion of 2 litres
• 0,0286 ug/kg*day + 0,0478 ug/kg*day = 0,0764 ug/kg*day (Water containing 1 ppb TCA)

Risk Characterization

• TCA is a relatively nontoxic chemical
• TCA does not appear to produce irreversible injury such as mutation, terata, or cancer
• Based on a lifetime continuous exposure, NOEL is 21 mg/kg*day
• With safety factor 10 used for each (1) variability in species, (2) variability in individual humans and (3) exposure to TCA from other sources, a nontoxic level of TCA in domestic water is estimated to be 270 ppb
• The by far highest level of TCA found on the area was 8800 ppb, which is still only approximately 1/30 of NOEL
• The second highest level of TCA was 150 ppb, which goes below the recommended