Ministry for the Environment chief operating officer Claire Richardson said there was no serious health risk, but it was being vigilant."
(Taken from https://www.radionz.co.nz/news/national/355654/toxic-foam-more-dodgy-water-supplies-discovered-in-manawatu)
The flame-retardants contain polybrominated diphenyl ether (PBDE), a chemical that is present in plastics, flame and can enter our body via the air we breathe, and the water we drink, or through soil contamination. If PBDE contaminate water supply at a particular site, then people who live around the site and derive their water supply from that site are at risk of developing health effects attributed to PBDE. The health effects attributed to PBDE include cancers of breast, prostrate, and kidneys, and for children who are exposed to PBDE, this includes drop in cognitive functions (such as drop in IQ scores). But does that mean that anyone exposed to any concentration of PBDE through any route will develop cancer or any child exposed to PBDE through any route will register a drop in their cognitive skiils score? The answer is no, and we will have to contextualise it to the local situation where such contamination occur. This is why we need to analyse as to how or why the Chief Operating Officer has declared that there was no serious health risk. You can run this exercise for yourself in every situation where you find yourself or your community being exposed to toxic foams or other contaminants. The process is referred to as environmental health risk assessment and it consists of four or five following steps (also see Figure 1):
  1. First step, identify the hazard (as we are doing here to identify that PBDE in firefighting foams is a hazard)
  2. Second step, assess the exposure in the "population" that is exposed to the toxin (in this case, for example, PBDE in the community)
  3. Third step, construct a dose-response curve or examine what do we know about the dose response pattern. This means for any amount of "dose" that is internally absorbed in the human body, construct what happens to the organs where they enter or how are they harmed. The higher the dose, the worse the case, so what exactly are the chances of harm?
  4. Fourth step, combine the exposure data from step two, and dose-response data from step three, and for the population under consideration, characterise the risk 
  5. Take steps to mitigate the risks by proper communication or arranging clean up or indeed anything that helps. 

Safety Assessment versus Risk Assessment

Depending on the health effect, an environmental health risk assessment can also be a safety assessment. When the health effect is one that does not cause cancer but something like heart disease or asthma, then EHRA essentially defaults to a safety assessment. In that form of assessment, EHRA exercise results in characterising a level of risk and a level of maximum allowable exposure so that no additional disease over and above a certain baseline results. The assessor accepts a certain level of exposure. On the other hand, when the health effect is one of cancer, then no theoretical upper limit of accepted level of exposure is possible, as cancer is a multi-step disease. At some point during the development of cancer, a molecular mechanism triggers the cancerous process and as this happens at molecular levels, therefore a theoretical low acceptable limit is impossible to define. Therefore in cancer, we usually do not define a threshold level but instead we define a level of exposure where certain amount of excess cancer cases accrue.

Steps of EHRA

EHRA consist of four steps: hazard identification, dose response assessment, exposure assessment and risk characterisation (Figure 1) Figure 1. EHRA four step process