Vol.
25 No. 5
September-October 2003
Significance
of Impurities in the Safety Evaluation of Crop Protection
Products
A.
Ambrus, D. J. Hamilton, H. A. Kuiper, and K. D. Racke
Pure
and Applied Chemistry
Vol. 75, No. 7, pp. 937-973 (2003)
Humans
can be exposed to pesticides and their impurities through
direct handling, re-entry of treated areas, contact with environmental
residues, and dietary intake.
Technical
pesticides, in addition to the "pure active ingredient," also
may contain complex mixtures of other minor chemical components
due to process variables, side reactions, and impurities in
starting materials. The impurities may contribute to the toxicity
of the pesticide or may alter the physical properties of the
product. For some impurities this may lead to the allocation
of maximum concentration limits in technical grade products.
The
toxicological tests carried out with technical products of
typical composition for registration purposes include assessment
of toxic potency of the impurities present in the test material.
However, the composition of the technical product may vary,
particularly with respect to impurities and potentially also
the toxicity of the product, depending on the manufacturing
process and sources of starting materials. The use of various
adjuvants and carrier materials in the preparation of the
formulation may also result in marked differences in storage
stability of formulations. This is especially of concern in
the case of generic pesticides, which may be produced and
formulated by many manufacturers under widely varying conditions,
with different materials, and under a range of quality control
standards.
Because
of the confidential nature of the information on impurities
in technical pesticides, this report cannot provide comprehensive
coverage of the extremely diverse subject. Rather, published
examples are given to illustrate possible scenarios and support
the conclusions and recommendations made This report is aimed
at improving the safety assessment of crop protection products
by focusing on the nature and effects of certain impurities.
Recommendations are provided to government authorities considering
the establishment or revision of their pesticide registration
and compliance programs to ensure the safe and efficient use
of pesticides. Guidance is also given for the correct assessment
of impurities in technical grade and formulated pesticide
products based on the technical documentation provided by
the manufacturer, appropriate utilization of FAO Specifications
of Plant Protection Products, and the toxicological evaluations
made by the FAO/WHO Joint Meeting on Pesticide Residues. The
importance of regular control of relevant impurities during
the manufacturing and formulating processes as well as during
storage and handling of marketed products is highlighted.
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