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Essential Pesticide Readings for Beginners (三)

1. Pesticide specifications

Pesticide Specifications are designed to define quality standards for pesticide products including technical materials (technical concentrates) and formulated products. Pesticide specifications encompass the physical appearance of the material, its content of active ingredient and any relevant impurities and its physical properties. They do not normally include chemical characteristics of the formulants unless they influence physical characteristics such as pH, acidity and alkalinity. Nor do they include efficacy information.

The worldwide adopted pesticide specifications are those set up by JMPS of FAO and WHO. These specifications provide an international point of reference against which products can be measured and judged thereby preventing the trade sale and use of inferior products. As part of their registration requirements some countries require that products permitted for use comply with the relevant FAO specifications.

However, JPMS does not have specifications for all the pesticide products. In China we also have our national standards and /or companies’ standards for many products. Most of the national standards have similar or identical requirements as JMPS specifications.

1.1 FAO specifications for technical products (TC) and technical concentrate (TK)

Technical grade pesticides are relatively pure active ingredients, used to prepare formulations.

TC = technical material; TK = technical concentrate

TC and TK are not clearly distinguished. TC is usually ≥900 g/kg with solvent(s) completely removed during synthesis and no solvent added subsequently.

Both TC and TK specifications have lower limits for active ingredient content.

(ii) FAO and WHO wish to encourage production of the highest purity active ingredients, because an increase in active ingredient content (say) from 900 g/kg to 990 g/kg in a TC will not significantly increase hazards due to active ingredient (because the content is raised by only 10%), whereas hazards associated with impurities may be greatly reduced (on average by a factor of 10 in this case).

(iii) The upper limit in a TK specification is to ensure that the TK hazard cannot be increased significantly (potentially by more than 10%), should the content of active ingredient be unexpectedly high.A good TC or TK should have:

(1) correct physical appearance; (2) not less than the minimum content of active ingredient; (3) not more than the maximum content of "relevant impurities"; (4) acceptable physical properties, if applicable.

The following clauses are included in FAO/WHO specifications for technical grade active ingredients:

TC and TK specification clauses are indicated in table 1 as below.

Item

Contents

Description

Physical appearance and chemical form (e.g. salt, ester) – simplest and most rapid test.

Stabilizer, if critical, is identified and a validated test method is provided.

If the identity and/or quantity of stabilizer is not critical, the clause indicates only that a stabilizer is present.

If a solvent is added (TK only), a clause and analytical method are not usually required for the solvent.

Identity

Unambiguous name … can be problematic for mixtures, especially if derived from plants or microorganism cultures – and also for some pyrethroids.

Primary identity test usually based on measurement of active ingredient content; back-up test required for cases of doubt.

If the active ingredient is a salt, ester or other derivative, it may be necessary to identify the derivative component.

No external validation of identification methods required, except

where the active ingredient is a mixture of defined ratio.  

Active ingredient content

Analytical methods validated by collaborative study.

Limit based on manufacturing specification, not 5-batch data.

Limit applies to the average of measured values.

Content expressed as g/kg, or g/l at 20ºC, of appropriate chemical

form (e.g. free acid, sodium salt, marker compound, etc.).  

Relevant impurity content

Analytical methods peer-validated in two or more laboratories.

Limit based on manufacturing specification, not 5-batch data.

Limit applies to the average of measured values.

Content expressed as g/kg, or g/l at 20 ºC.  

Other clauses

 

Acidity, alkalinity or pH range, if required.

Other characteristics, if critical for TC, TK or formulation quality.

Storage stability is not specified, because manufacturers can usually

re-purify an aged TC or TK.

If a TC or TK is sold to end-users as a “formulation” (e.g. certain UL), the formulation specification applies and storage stability is specified.

An example FAO specification for glyphosate TC:

1 Description

The material shall consist of glyphosate, together with related manufacturing impurities. It shall be a white dry powder, free from visible extraneous matter and added modifying agents.

2 Active Ingredient

2.1 Identity tests (284/TC/(M)/2, CIPAC Handbook 1C, 1985, p. 2132)

The active ingredient shall comply with an identity test and, where the identity remains in doubt, shall comply with at least one additional test.

2.2 Glyphosate acid (284/TC/(M)/3, CIPAC Handbook1C, 1985, p. 2132)

The glyphosate acid content shall be declared (not less than 950 g/kg) and, when determined, the mean measured content shall not be lower than the declared minimum content.

3 Relevant Impurities

3.1 Formaldehyde (Note 1)

Maximum 1.3 g/kg of the glyphosate acid content found under 2.2.

3.2 N-Nitrosoglyphosate (Note 2)

Maximum 1 mg/kg 1.2 FAO Specifications for Formulated Products

Scope of formulation specifications: Similar to TC and TK specifications but also specify physical properties and synergist (if applicable). Essential additives for safety or stability. Unlike JMPS, national authorities should control formulants. For example in USA and Lebanon, some formulants and /or solvents are not allowed to be used in formulated products.

Specifications for mixed active ingredients and formulations: In most cases, separate specifications apply to each active ingredient. SE, ZC, ZE, ZW are treated differently because of the complexity of these products.

Where the ratio of active ingredients is critically important, a specification may be developed for an individual formulated product. Where two or more solid formulations are mixed, expanded tolerances for active ingredient content take account of the tolerance on formulation ratio and increased heterogeneity.

The contents of a formulation specification include description clauses, active ingredients, relevant impurities, physical properties, low temperature stability, high temperature stability, etc. The explanations to each of the above items of a specification are indicated in table 2.

For formulated products, FAO sets up tolerances for different contents of active ingredients, which are shown in table 3. As above mentioned, for TC products, the actual test result should not be lower than the declared content. However, the tolerances set for different contents of active ingredients in formulated products are also used for TK products.

The parameters (physical properties) given for each of the major formulations and the recommended testing methods (CIPAC) for the parameters are indicated in appendix 8.

Table 2  Contents of Specifications for a Formulated Product 

Items

Explanations

Description clause

•Physical appearance of product and chemical form of the active ingredient.

•Provides a simple and rapid means to determine compliance.

•Corresponding TC or TK specification is referenced.

Active ingredient identity and content

•Test methods similar to those for TC and TK, but extraction (and purification for identification) of active ingredient may be required.

•May be necessary to identify the counter-ion, etc., if it is critical for product stability or performance.

•Analytical test methods for determination of content validated by international collaborative study, to provide evidence of the reliability of the methods and the data provided.

Tolerances for active ingredient content in formulation

 

Refer to table 3 as below.

Relevant impurities

Criteria as for TC and TK but insolubles (particulates) and acidity/alkalinity are treated as physical properties. 

Limits usually based on active ingredient content but may be higher if concentrations can increase in storage or through reactions with formulants.

An impurity relevant in TC or TK may become non-relevant in formulations containing only low levels of active ingredient, e.g. if the impurity concentration is diluted to a level too low to measure.

Physical properties

Specified properties are the minimum to distinguish good and bad products.

Clauses and limits may differ from FAO/WHO guidelines, if justified for a particular product.

Test methods for physical properties are simple models; they do not demonstrate field performance.

Results are method-dependent, so test methods must be performed exactly as described.

If the test method for a physical property has not been suitably validated and/or published, the specification cannot be developed.

Low temperature storage stability

•Storage test at 0 ºC required for liquid formulations, which may grow crystals, aggregate particles or develop separate phases.

CS formulations may require freeze-thaw test to show that capsules are not weakened by freezing.

High temperature storage stability

 

Test required for all formulations.

•Simulates two years’ storage under “cool” conditions.

•Standard requirement is 54 ºC for 14 days.

If 54 ºC is not appropriate for the product, alternative conditions are:

•45 ºC for 6 weeks

•40 ºC for 8 weeks

•35 ºC for 12 weeks

•30 ºC for 18 weeks.

Post-storage tests required

•Active ingredient content – usual minimum is ≥95% of pre-storage level.

•Relevant impurities, if they could increase in storage.

•Physical properties, if they could worsen with storage.

Table 3 Tolerances for content of active ingredient in TK and formulate products

Declared content (g/kg or g/l)

Tolerance

up to 25

 

above 25 up to 100

above 100 up to 250

above 250 up to 500

above 500

± 15% for “homogeneous” products (e.g. EC, SC, SL)

±25% for “heterogeneous” products (e.g. GR, WG)

± 10% g/kg or g/l

± 6% g/kg or g/l

± 5% g/kg or g/l

± 25 g/kg or g/l

2. Pesticide quality control

Pesticide specifications or standards are the basis of quality control. The quality control is very important for international pesticide business. Pre-shipment analysis of pesticide consignments will ensure that the product offered meets the relevant specifications before shipment, thereby avoiding subsequent problems if the product delivered is of poor quality. Quality control on arrival or after shipment may be required if the traceability of the product cannot be guaranteed, if the product appears to have been tampered with or if it is known to have been exposed to unacceptable shipping and storage conditions. 

Normally a quality control program consists of the following items

(1) Analysis of the active ingredient(s);

(2) Analysis of relevant impurities;

(3) Testing of physical properties;

(4) Testing of storage stability at elevated temperature and at low temperature.

Those items are set in FAO specifications for individual product and different formulation types.

For obtaining reliable testing results, the qualification of the laboratory and the quality assurance system that the laboratory adopts are extremely important.

The laboratory must have available the full range of validated test methods as controlled documents. These may be generated and validated in-house, but at least should be based on appropriate CIPAC or AOAC procedures. It is recommended that, wherever possible, methods used should have been demonstrated to be sufficiently robust, through collaborative study, and for referee purposes. CIPAC or AOAC approved methods should be used exclusively-or ASTM methods for some physical characteristics.

Where it is necessary to develop in-house procedures, these should be carefully validated, in accordance with generally accepted validation schemes (e.g. the Sanco Document 3030) before being applied to test samples.

It is strongly recommended that where methods are to be applied for the first time in the laboratory, or by an operator who is unfamiliar with the procedure, a previously analysed sample should be checked in replicate, to ensure adequate accuracy and precision.

Where impurity profiles of technical materials are being determined, it is important that methods should include details on the use of blanks and spiked samples, to check for possible interference, and on levels of recovery, which should be carefully defined. Such checks must be carried out prior to analysis, and the recovery and other defined criteria fully met.

In most cases, products should be checked against the appropriate specification, either provided by the manufacturer or the WHO or FAO specification. If none of these is available, it is essential that appropriate tests be applied, as indicated for each product type in the Manual on the Development and Use of FAO and WHO Specifications for Pesticides.

An indication of acceptable ranges for some of the standard tests may be found within this document, or by referring to FAO and WHO specifications for similar product types. Alternatively, specifications provided by reputable manufacturers may be used.

In addition to the test methods described earlier, laboratories will require standard operating procedures for all key activities undertaken, which should be held as controlled documents. In particular, procedures will be required to cover the following:

• sample receipt, handling and storage, including use of expiry dates;

• calibration programme and check requirements on specific instruments;

• procurement, storage and use of analytical standards and other calibration materials;

• storage, use and disposal of reagents and test solutions (including control of expiry dates);

• equipment cleaning protocols;

• selection of new equipment and suppliers;

• procedures for data processing and storage of electronic information;

• maintenance programmes and procedures;

• standard operating procedures for all laboratory equipment.

Careful management of all samples and stock solutions is vital, with good labelling and strict adherence to shelf-lives.

It is also important for laboratories to develop and document procedures for dealing with disputes concerning analytical data, rather than operating on an ad hoc basis. Rapid resolution can often be achieved by dialogue between laboratories, sharing of information and data, and where appropriate retesting and swapping of samples