General list of impurities and classes of impurities of toxicological concern

The APVMA has overall responsibility for the regulation of active constituents used in agricultural and veterinary chemical products. Section 14 of the Agricultural and Veterinary Chemicals Code (Agvet Code) requires that, before granting an application for the approval or registration of  a chemical product, the APVMA must be satisfied with regard to the matters mentioned in subsection 14(3)(e)—that is, that the use of the active constituent or chemical product will not have a harmful effect on human health, the environment, occupational health and safety or trade, and that the product is effective for its intended use. In particular, the APVMA is required to separately approve active constituents. An integral part of the evaluation process for an active constituent is the assessment of its chemical composition.

To a large degree, the safety, efficacy and environmental impact of agricultural and veterinary chemical products are dependent on the composition of the active constituents. When each active constituent completes the approval process, the APVMA establishes a standard for it. The standard typically specifies the minimum purity of the active constituent, the ratio of isomers to diastereoisomers where relevant, and the maximum level of the relevant impurities, including those of toxicological significance. The toxicological profile of the active constituent is directly linked to its purity and the associated impurities.

A condition of registration of an agricultural chemical product is that its active constituent(s) must meet the APVMA standard when the product is supplied for sale. Products are tested against the standard as part of the registration process.

For a chemical product to be approved or registered, neither its mean measured active constituent content nor the active constituent analysis of any individual batch can be lower than the minimum purity specified in the standard for each active constituent. Where the standard is for an impurity, maximum criteria apply. Where an active constituent has a number of possible isomeric forms, the overall purity of the active constituent, as well as the relative amounts of isomers, may be important. Differences in the relative proportions of the isomeric forms of an active constituent can, and often do, have toxicology and efficacy consequences. Where the isomeric composition of an active constituent is toxicologically relevant, this information is included in the standard for that active constituent.

In some cases, the active constituent is not isolated, and a manufacturing concentrate is prepared by adding non-active (inert) constituents such as solvents, stabilisers or both. For most manufacturing concentrates it is not practical to recommend a standard for the active constituent content because the amount of active constituent present in the material can be varied by dilution or concentration. The active constituent content alone does not necessarily reflect the overall quality of the manufacturing concentrate. Batch analysis data on the manufacturing concentrate are required to ensure that undesirable impurities are not present in the manufacturing concentrate. The manufacturing concentrate must also meet the relevant standard of the non-manufacturing concentrate on a dry weight basis.

In addition to the instances where maximum impurity standards are listed for specific active constituents, the APVMA maintains a general list of impurities and classes of impurities of toxicological concern. As these impurities can have an adverse impact on human health, the environment or both, the APVMA requires that registrants provide information on their identities and concentration in the active constituent.

The list follows.

  • Anilines and substituted anilines
  • Dimethyl sulphate
  • Dichlorodiphenyltrichloroethane (DDT) and DDT-related impurities
  • 2,3-diaminophenazine (DAP) and 2-amino-3-hydroxyphenazine (AHP)
  • Ethylene thiourea (ETU) and propylene thiourea
  • Halogenated dibenzodioxins and halogenated dibenzofurans
  • Hexachlorobenzene (HCB)
  • Hydrazines and substituted hydrazines
  • Methyl isocyanate
  • Nitrosamines
  • Oxygen analogues of organophosphates
  • Polychlorinated biphenyls (PCBs)
  • O,O,O’,O’-tetraethyl dithiopyrophosphate (S,S-TEPP or Sulfotep) and O,O,O’,O’-tetraethyl monothiopyrophosphate (O,S-TEPP)
  • Sulfoxides and sulfones of organophosphates and carbamates
  • 3,3’,4,4’-tetrachloroazobenzene (TCAB) and 3,3’,4,4’-tetrachloroazoxybenzene (TCAOB)

If you have any queries concerning the standards for active constituents, please contact:

Pesticides chemistry

Phone: +61 2 6210 4748
Fax: +61 2 6210 4840

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