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HRA trial results: low arsenic bioavailability at Moanataiari

15 July 2012

Moanataiari Update # 35: The Health Risk Assessment (HRA) trial report is now available and the preliminary results show that the bioavailability of arsenic is less than 10%.

The trial also shows lead at 70% bioavailability for properties with over 300 mg/kg (parts per million) of lead in their soils.

"The National Environmental Standard (NES) assumes that 100% of the arsenic and lead will be absorbed by the body if soil is ingested, which is one of the factors the NES contemplates when it sets conservative standards for arsenic and lead in soil" said Communications Manager Benjamin Day.

"However, if the bioavailability for these elements is lower than 100%, then this could increase the risk threshold and therefore the remediation criteria could also be higher than the NES standards".

Golder Associates, the company that conducted the trial, indicate in their report that the guideline value for arsenic could be up to 78ppm, from the national standard of 20ppm and for lead the value could be up to 280ppm, from the national standard of 210ppm.

"These early results are encouraging for the folks of Moanataiari. Lower than expected bioavailability probably means less risk to human health and could also mean less intrusive remediation options are required for some properties" said Mr Day.

At their next meeting to be held on Wednesday 1 August 2012, the Governance Group will consider the Golder report and decide if the project will proceed with a full Health Risk Assessment (HRA). A full HRA would ensure the bioavailability science and results are more robust (more properties would be sampled) before the Governance Group finalise any decisions on remediation options.


Phase 2 average results for private property tested at Moanataiari

 

National Environmental Standards 
  • Arsenic = 20ppm (assumes 100% bioavailability)
  • Lead = 210ppm (assumes 100% bioavailability)
HRA Trial (initial indications for possible guidelines)
  • Arsenic = Up to 78ppm (based on initial HRA findings of 10% bioavailability)
  • Lead = Up to 280ppm (based on initial HRA findings of 70% bioavailability)
Western zone* average results
  • Arsenic = 77ppm
  • Lead = 78ppm
Eastern zone* average results
  • Arsenic = 259ppm
  • Lead = 287ppm

*East and West of Moanataiari Street.


Remediation options workshops

The project team are conducting the first series of workshops this week with Moanataiari residents and property owners to start discussing possible remediation options.

"While final decisions about the remediation options for properties cannot be made until the HRA process is completed and fully understood, it's still a good idea to start looking at a full range of options with residents so they can engage with us in meaningful dialogue when it comes to the decision-making time for remediation".

"It's also important that we gain an understanding of some of the challenges and opportunities that only residents and property owners can tell us; the project team don't hold a monopoly on coming up with good ideas, so the workshops create further opportunity for us to have important two-way conversations" said Communications Manager Benjamin Day.

Key facts about bioavailability

  • Bioavailability simply means how much of the arsenic in the soil (if ingested) is actually absorbed by the body
  • The National Environmental Standards (NES) assume the arsenic and lead in the soil is 100% bioavailable once ingested, which is part of the formula used to get to the standard of 20ppm (arsenic) and 210ppm (lead) for residential properties
  • If the bioavailability of arsenic and lead in the soil is low (e.g. 10%), this could increase the risk threshold and therefore the remediation criteria could be higher than the NES standard of 20ppm (arsenic) and 210ppm (lead).
  • If the bioavailability of arsenic and lead in the soil is high (e.g. 80%), this could reduce the risk threshold and therefore the remediation criteria could be closer to the NES standard of 20ppm (arsenic) and 210ppm (lead).