I. Introduction
The New Zealand Waste Strategy, published in March 2002, is a long term strategy to help reduce waste, recover resources and better manage residual waste in New Zealand. It covers solid, liquid, gaseous and hazardous waste. The context of this study is policy development designed to deliver the strategy. Specifically, in order to ensure that efforts are directed to wastes where the most benefits can be obtained, and are directed in a manner that best achieves those benefits, it is important that the current state of knowledge regarding the environmental and health impacts of wastes is considered and collated. Waste electrical and electronic equipment (WEEE) is a diverse waste category, and international opinions regarding the impacts of various substances contained within WEEE vary. This study considers the quality and weight of scientific evidence and reports on the state of knowledge regarding both consensus and diversity in scientific opinion pertaining to these impacts, both internationally, and as applicable to New Zealand.
II. Review Section
Any substance is potentially toxic if the dose and duration of exposure are sufficiently high. However, there are many ways in which chemicals might disrupt the functioning of an organism, including corrosive or irritant effects, acute and chronic toxicity, effects on the nervous system (neurotoxicity), impairment of the reproduction of cells or organisms (by carcinogens, mutagens or reproductive toxins), or damage to hormone systems, for example, the effects resulting from endocrine-disrupting chemicals (RCEP, 2003). Tests have been devised to assist in determining toxic doses - i.e. doses required to cause a specified impact on health of humans or other living organisms. The major sources of uncertainty in toxicity testing include the difficulty in envisaging all important possible impacts, and in modeling or otherwise determining the conditions under which the relevant doses are likely to be applied. Regarding the former, the relatively recent realisation that endocrine disruption is important is a reminder that there may still be impacts that have yet to be recognised, and for which tests have not yet been developed. Regarding the latter, in general, tests are devised which are intended to take a conservative approach in identifying 'worst case' scenarios of doses, accompanied by risk assessment based upon comparing the estimates of concentration in different conditions.
It is well-documented that toxicity is not solely a characteristic of synthetic chemicals (e.g. RCEP, 2003). Some of the most toxic substances known occur naturally in organisms, where they usually form part of a defence mechanism. For example, many plants, including common ones such as clovers, produce hydrogen cyanide when damaged, and a number of Australian plants produce fluoroacetate, a respiratory inhibitor which is highly toxic to sheep, but to which red kangaroos have adapted. Therefore, in devising toxicity tests, and levels of exposure above which toxicity is deemed to cause an unacceptable impact, due cognisance must be paid both the natural and synthetic substances, and to the conditions of the receiving environment. Characterisation of the dose-response relationship is thus a process of identifying the concentration and time of exposure required to produce a specific impact outcome, or response. Hence, we can talk of the dose-response relationship between airborne lead from vehicle exhausts (assuming leaded petrol) and the response in terms of child brain development impact. Of course, the dose for another response, such as death of roadside vegetation, will be different. In WEEE-relevant substances, it is important to note that the form of the waste and the conditions of its storage or burial will be important in determining both the dose and the response. As there are a wide variety of landfill conditions,