Phase 3 - Health Risk Assessment

The Health Risk Assessment has been completed and can be downloaded on the right-hand side of this page from the download box.

Health Risk Assessment

The HRA has been completed and can be downloaded by clicking on the link in the download box on this page.

This document, among others, will now feed into the final report and assessment of remedial options for the Governance Group to make recommendations on what the next steps will be to mitigate or manage the risks presented at Moanataiari.

The Governance Group meet on 5 December to consider the "next steps".

Increased risk to health at Moanataiari known - bioavailability work completed

The potential increased riskat Moanataiari has been defined, now that the bioavailability study has been completed and the new 'standard' for arsenic is 50ppm(up from the national standard of 20ppm because of the low bioavailability).

The Government has a policy that the "acceptable" increased risk of developing cancer from living on contaminated soil is 0.001% or 1 in 100,000.

That means living on soil with arsenic levels of 50ppm at Moanataiari gives a person a 0.001% additional risk of developing cancer.

Here are the additonal risks (above the national policy of 0.001%) at Moanataiari relating to the key contaminant of concern, arsenic.

  • For Blocks 5 & 6 comprising 83 properties, there is no additional risk
  • For Block 7 comprising 15 properties, the additional risk is 0.00032%
  • For Block 8 comprising 26 properties, the additional risk is 0.00082%
  • For Block 4 comprising 16 properties, the additional risk is 0.00116%
  • For Block 1 comprising 23 properties, the additional risk is 0.00208%
  • For Block 3 comprising 22 properties, the additional risk is 0.00252%
  • For Block 2 comprising 12 properties, the additional risk is 0.00398%

* The darker patches on the map in blocks 1 and 4 don't relate to arsenic and relate to levels of other contaminants like lead, which will be discussed in the HRA document and with property owners very soon.

Download the map here

The Health Risk Assessment will outline various options about how we can reduce or manage this risk.

Phase 3 background information


Phase 3 originally involved testing the greater-Thames area (in the hills) to establish natural background levels of arsenic, which was to help us develop mitigation measures that were appropriate for Moanataiari.

However, the results from Phase 2 have revealed levels of arsenic and other elements that are much higher, in many instances, than the various national standards, making the background testing phase less relevant for the protection of human health.

The Governance Group have reaffirmed that human health is the main focus for the project, so have approved a full HRA programme (focusing on the bioavailability of contaminants found to be above national standards)

How might the HRA impact the project?

The HRA will help the team understand how much arsenic and other contaminants could be absorbed by the body (bioavailability) so we can better understand the real risk to human health before finalising the Phase 4 work (remedial options planning).

Please visit the project plan web pageto find out more about the timelines for Phase 3. 

Key facts

  • Bioavailability simply means how much of the arsenic in the soil (if ingested) is actually absorbed by the body
  • The HRA results might not be as relevant to the eastern zone because the contamination is much higher there than it is in the western zone
  • The National Environmental Standards (NES) assume the arsenic in the soil is 100% bioavailable once ingested, which is part of the formula used to get to the standard of 20ppm figure (arsenic) for residential properties
  • If the bioavailability of arsenic in the soil is found to be low (10-20%), this will increase the risk threshold and therefore the remediation criteria will be higher than the NES standard of 20ppm
  • If the bioavailability of arsenic in the soil is found to be high (80-100%), this will reduce the risk threshold and therefore the remediation criteria will be close to the NES standard of 20ppm

With these points in mind, the HRA will therefore be able to assist the project in the generation of remediation criteria and management/remediation options for Phase 4 of the project.

What's the difference between bioavailability and bioaccessibility?

For this project bioavailability refers to how much arsenic is actually absorbed by the body (as opposed to just passing through the body). Because we can't test on animals or humans to find the bioavailability of arsenic, scientists test for 'bioacessibility' in a lab (how much arsenic they can measure from the soil in a lab situation).

Phase 3 of the project is testing for the bioaccessibility of arsenic in a lab environment for the project team to make a decision on how bioavailable arsenic might be in the soil at Moanataiari.

20 parts per million arsenic - assumptions explained

At a recent community forum, the residential standard for arsenic was discussed (20 parts per million).

Members of the forum requested a plain-English explanation regarding some of the underlying assumptions that were made to formulate the national environmental standard.

The standard assumes:

  • That all of the arsenic is absorbed by the body if the soil is eaten (100% bioavailability)
  • A person's weight at 70kgs
  • That 10% of produce (fruit and veggies) consumed are grown at home
  • A life expectancy of 75 yrs
  • A person spends 350 days a year at the site (residential exposure frequency)