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TCA in groundwater

TCA in groundwater. Anne Karvonen Juha Villman Mikko Pohjola. Introduction. Focus: 1,1,1-Trichloroethane in Groundwater Scope: Santa Clara Valley (Silicon Valley) in California TCA hazard to humans Other exposures, besides exposure to TCA in groundwater taken from wells, excluded

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TCA in groundwater

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  1. TCA in groundwater Anne Karvonen Juha Villman Mikko Pohjola

  2. Introduction • Focus: 1,1,1-Trichloroethane in Groundwater • Scope: • Santa Clara Valley (Silicon Valley) in California • TCA hazard to humans • Other exposures, besides exposure to TCA in groundwater taken from wells, excluded • All data from an article with abovementioned title, written in the 80's

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

  4. 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 • NOEL for lifetime continuous exposure for humans estimated as 50 ppm (factor 5) • Equals to 21mg/kg*day (weight 70 kg, breathes 18 m3/day)

  5. 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) • Total dose • Worst case exposure: 1 bath per day + staying in 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)

  6. Risk characterization • TCA is a relatively nontoxic chemical • No irreversible injury such as mutation, terata, or cancer • Can cause narcosis, mild liver injury, and irritation of the respiratory tract (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 • Highest level found (8800 ppb) still only 1/30 of NOEL • The 2nd highest level (150 ppb) below the nontoxic level • Estimate includes a large safety margin, but considering the uncertainties one should aim for lowest practical dose levels anyway

  7. Thank you! • Questions?

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