Publications: Research reports and publications

Ecotoxicity review of 26 pesticides

27 August, 2013
Cawthron Report 2357. Prepared for Nelson City Council.


The Nelson City Council (NCC) is in the process of submitting a resource consent application to use a range of pesticides for the control of vegetation and pests on NCC administered parks and reserves. The Council has contracted Cawthron Institute (Cawthron) to review the ecotoxicology of 26 pesticides being considered as part of their application.

To characterise environmental risk of the 26 pesticides, the main international databases (i.e. data from World Health Organisation (WHO) Pesticide Data Sheets (PDSs), US Environmental Protection Agency (ToxNet and PAN), European Chemicals Agency (ECHA), Canadian (Health Canada), AGRITOX database on plant protection substances (France), Australian and New Zealand Environment and Conservation Council (ANZECC) and Rotterdam Convention database of chemicals) were reviewed and the most relevant information collated into this report. To simplify the interpretation of the data, the findings from the review have been summarised in Table 1.

A classification framework has been adapted using a scoring system (see e.g. McBrien,1987; and the description of the system of scoring in the Explanations section) for the purpose of assessing the environmental risk of each pesticide. Parameters are weighted to reflect their relative importance to the risk characterisation of each pesticide, which is then allocated a score that is depicted as a colour e.g. low risk (green), medium risk (yellow) and high risk (red).

The colour ranking allocated for each pesticide is based on key indicators including:

  • threshold concentration for the 95% protection level of species (hazardous concentration 5%; HC5)
  • the physico-chemical properties of the chemical (potential to bioaccumulate and persistence in the environment)
  • regulatory status in other countries.

When the protection level was uncertain or when the chemical was either not approved (e.g. pending renewal) or banned for use in at least one country, a medium risk ranking (yellow) was applied as a precautionary measure.

This colour ranking of each pesticide in Table 1 provides an 'at-a-glance' summary of the relative potential environmental risk, for example a green-ranked pesticide may potentially have less environmental impact than a pesticide allocated a yellow or red ranking. But this should not be interpreted as an endorsement for its unrestricted use. These rankings are based on current information pertaining to risk characterisation, but do not take into account the following:

  • local environmental conditions and potential receptor species
  • field application rates
  • application timing
  • formulation used.

In addition, the stability of the pesticides in water does not take into account the fate of degradation products and their potential toxicity. So these pesticide rankings should be used as a starting point to a full risk assessment.

This review confirmed of the 26 pesticides assessed, five pesticides were banned for use in at least one country (either for human health and / or environmental reasons): 2,4D(Norway), chlorpyrifos (Saudi Arabia), mecoprop (Thailand), MCPA (Thailand), and MCPB (Thailand).

The Rotterdam Convention assists Parties to reduce risks from certain hazardous pesticides in international trade. The current list of pesticides registered with the Rotterdam Convention includes over 6,000 chemicals. A recommendation as a result of this review is that NCC could consider updating the list of pesticides in their resource consent application to include some of those on the Rotterdam Convention list. These may provide more sustainable alternatives to the current pesticides NCC uses.