TCA in groundwater

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. All data from the abovementioned article written in the 80's.

Identification of Hazard

Fate in body

• TCA is absorbed efficiently (~100%) from the gastrointestinal tract and approximately with 30% efficiency from the lungs
• Chemical is rapidly distributed to all tissues via bloodstream
• Inhaled (uptaken) and ingested chemical assumed to behave/affect similarly in body

Acute toxicity (human volunteers)

• Mild eye irritation
• Narcosis

Subchronic toxicity

• Reversible irritation of respiratory tract
• Fatty liver
• Narcosis
• Dermally reversible irritation at the site of application

Chronic toxicity, incl. carcinogenicity

• 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

Genotoxicity

• Only few weakly positive results for mutagenicity of TCA
• These results can be explained by butylene oxide present in some commercial formulations of TCA

Reproductive and developmental toxicity

• No teratogenic effects in rodents exposed to TCA

Conclusion

• Relatively nontoxic chemical
• Narcosis, mild organ pathology and irritation of respiratory tract
• Effects appear only at vapor exposures > 250 ppm

Dose-Response assessment

Acute strong exposure

• 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

Chronic exposure

• Threshold assumed (no effects below a certain dose)
• NOEL for lifetime continuous exposure for humans estimated as 50 ppm (factor 5)
• Equals to 21mg/kg*day (human weight 70 kg, breathes 18 m³/day)

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 of exposure

• Ingestion of contaminated water
• Dermal contact with contaminated water (bath, shower)
• Dermal contact with vapors volatilizing from the surface of contaminated water (bath, shower)
• Inhalation of vapors volatilizing from the surface of contaminated water (bath, shower, toilet)

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
• Narcosis, mild liver injury, and irritation of the respiratory tract are the notable toxic effects (reversible)
• With safety factor of 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 is below the recommended nontoxic level assuming e.g. life-time exposure
• Given nontoxic level estimate includes a large safety margin, but considering the uncertainties one should aim for lowest practical dose levels anyway