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The problem of obsolete pesticides

1.1 When are pesticides obsolete?

   Obsolete pesticides are defined as stocked pesticides that can no longer be used for their original purpose or any other purpose and therefore require disposal. Common causes of this situation include the following:

   A product has deteriorated when:

   In some publications, obsolete pesticides are also correctly referred to as pesticide waste. Another term used is unwanted pesticides, a broader definition than obsolete pesticides. Besides obsolete pesticides (the ones that definitely cannot be used any longer and require disposal), it also covers pesticides that, in principle, could still be used, but are not being used and are regarded as unwanted by their owner because there is a surplus stock in excess of requirements; the pest problem has passed; there are logistical constraints concerning distribution; the formulation is not suitable for the application equipment, etc. Although there is no immediate use for these products, they may still be in good condition and may be potentially usable without compromising environmental or occupational safety. Such products should not be regarded as obsolete so long as it has not been established that there are no solutions to the impediments hindering their use (such as more effective distribution, repackaging, procurement of different application equipment or reformulation of the product to make it usable with available application equipment, or alternative use). Therefore, unwanted pesticides are not necessarily obsolete. However, stocks that in principle are still usable, but are not being used, run a high risk of becoming obsolete as a result of prolonged storage.
   Figure 1 represents a decision tree to determine whether pesticides are obsolete.


FIGURE 1 - Decision tree to determine whether pesticides are obsolete

   It is not always easy to establish whether old stocks have deteriorated to a level at which they have become unusable. If not stated otherwise on the label, products normally have a shelf-life of two years from the date of release, during which the manufacturer guarantees the quality of the product, provided that it is stored according to instructions precisely stated on the label. Such instructions may for instance refer to temperature, humidity and light/exposure to direct sunlight. Storage periods beyond two years, or beyond the shelf-life indicated on the label, do not automatically imply that such products have degraded beyond usability. Pesticides can often be stored for much longer than their indicated shelf-life. On several occasions, analytical results showed that five- to seven-year-old stocks of organophosphates, with an indicated shelf-life of two years, were still usable. However, the opposite may also occur. Storage under extremely high temperatures may accelerate deterioration to such an extent that the product becomes unusable before expiry of its shelf-life. For example, a temperature rise of 10C may increase the decomposition rate by a factor of two or three (GIFAP, 1985). Temperatures inside shipping containers or in poorly ventilated stores may easily reach 40C or higher when exposed to direct sunlight in tropical environments. High humidity, direct exposure to sunlight and strong temperature fluctuations may also shorten the actual shelf-life. This will depend on a number of factors that cannot always be controlled, monitored or predicted, which is why labels normally state the date of manufacture/release, instead of an expiry date. Labels may also state a "date of test", a date when analytical results confirmed that the product has not deviated from its original specifications, or that deviations are within an acceptable range.


FIGURE 2 - Abandoned pesticide containers (barrels) blown close to disintegration by the high pressure of
obsolete pesticides kept in them for years

   Products that have deteriorated as a result of physical changes may be identified without difficulty: originally clear liquid formulations may have formed flakes, crystals or an emulsion; emulsions may have precipitated and solidified against the container's inside wall; powders may have solidified after becoming damp. More difficult to identify are products whose chemical properties have changed, while the visible physical properties remain unchanged. In such cases, it is often necessary to conduct chemical analysis in a laboratory to establish whether the product is still usable. The FAO specifications for plant protection products provide guidance on permitted tolerances for active ingredient contents, impurities and physical properties (FAOa, in preparation).
   In some cases, a decline in active ingredient concentration may be compensated by a proportional increase in application volume, provided that the decomposition products of the active ingredient do not increase the product's toxicity beyond acceptable margins.
   The Basel Convention on the Control of Transboundary Movements of Hazardous Wastes and their Disposal, 1989 (UNEP/SBC, 1994) defines "wastes"as "substances or objects which are disposed of, or are intended to be disposed of, or are required to be disposed of by the provisions of national law". Obsolete pesticides fall into this category. International transport of obsolete pesticides is therefore governed by this Convention. In addition, obsolete pesticides are subject to several international conventions regulating the transport of dangerous goods1, which are all based on the UN's Recommendations on the transport of dangerous goods (UN, 1991). National regulations governing the transport and handling of hazardous substances may be more strict on hazardous waste than on pesticides.

1.2 Occurrence and state of obsolete pesticide stock

   Obsolete pesticide stocks are present in the majority of developing countries. Quantities in individual countries range from a few tonnes to several thousands. In 1994, FAO conducted an inventory of obsolete pesticide stocks in Africa and the Near East. Results of this inventory indicate that the total of obsolete pesticides in Africa probably exceeds 15,000 tonnes2. In 1993, at least three Asian countries were known to have quantities of obsolete pesticides within the range of 5,000-10,000 tonnes each. Unconfirmed figures from Eastern European countries suggest that several countries hold very large quantities. The total in non-OECD countries may be well in excess of 100,000 tonnes. In addition, there are large quantities of heavily contaminated soils that should be regarded as hazardous waste.
   Common types of obsolete pesticides include organochlorine compounds such as DDT, dieldrin and HCH, which have been withdrawn or banned for human health and/or environmental reasons. Countries in the migratory locust zone often still have large quantities of these compounds remaining from old strategic stocks for locust control. Several of these stocks were acquired over 20 years ago.
   Another large group is organophosphates and carbamates that have deteriorated as a result of prolonged or improper storage. Examples of commonly found products that have deteriorated beyond usability include: dimethoate, fenitrothion, malathion, carbaryl and propoxur.
   In many cases, obsolete pesticides are stored under conditions that do not meet the basic standards for safe and responsible storage of such hazardous materials. Stores are often poorly ventilated or do not have concrete floors. At many locations, obsolete pesticides have even been stored in the open. Bags are often torn or deteriorated. Drums are often corroded or have ballooned as a result of heat and leaking drums are a common feature. In some cases leakage has been so bad that floors of stores are completely covered with pesticides. Many stores lack basic provisions to deal safely and adequately with leakage or other emergencies.

1.3 Causes of accumulation of obsolete pesticides

   There are many factors that have contributed to the formation of the present stockpiles of obsolete pesticides. These factors can be grouped roughly into the following categories:

   A detailed analysis of the causes of accumulation of obsolete pesticide stocks is provided in Chapter 2.

1.4 Hazards connected to obsolete pesticides

   Leaking drums and torn bags can seriously affect the occupational health of staff working at the storage site and of others who happen to come in contact with the pesticides. They often pose a broader general danger to public health and the environment. Factors determining the level of hazard include:

   Contamination of groundwater or soil can occur through seepage of leaked pesticides into the ground or runoff during heavy rains. Poisoning of people or animals can occur through direct contact with the product, inhalation of vapours, drinking of contaminated water, or eating of contaminated food. Other hazards include:

1.5 Disposal of obsolete pesticides

Disposal options

   Products that can no longer be used are to be disposed of in a safe and environmentally sound manner. In most cases, the recommended method will be high-temperature incineration. Developing countries do not generally have appropriate high-temperature incineration facilities for hazardous waste. This means that obsolete products may have to be shipped to special hazardous waste incineration plants in countries that are willing to accept the waste. The costs of repackaging, shipment and incineration are high and the administrative procedures to comply with international conventions concerning the shipment of hazardous waste may be complicated and time-consuming. Alternative high-temperature incineration methods such as the use of a mobile incinerator or a local cement kiln have their limitations and are often not applicable in a safe and/or cost-effective manner3.


FIGURE 3 - A cocktail of obsolete, banned and unwanted pesticides. Powder pesticides spill from torn jute and
paper bags, blowing into the environment or mixing with heavily leaking liquid pesticides kept in tin cans,
barrels, etc. in the background. Since pesticides are in the open, accessible to passers-by, handlers and staff,
exposure casualties are always common and widespread

   Methods such as chemical treatment or landfilling after solidification may sometimes offer solutions for relatively small quantities of specific groups of pesticides. Other methods are not recommended. Pesticides should never be disposed of by burying or open burning.
   For detailed information concerning disposal options, reference should be made to the Guidelines on disposal of bulk quantities of pesticides in developing countries (UNEP/FAO/WHOa, in preparation).
   Safe and environmentally sound disposal of pesticides can be very expensive. Costs depend on the disposal method, the total quantity of pesticides to be disposed of, the type and variety of products, the number of locations from where pesticides are to be removed, the distance to a port of exit, the degree of contamination, and so on. In 1993, the cost of a complete clean-up operation comprising repackaging, shipment and incineration of a bulk quantity of a single product from one location in a landlocked African country was in the order of US$4,000 per tonne. Costs of removing a variety of products that are to be collected from several locations will be even higher.Donor assistance to disposal operations

   Aid agencies may be willing to provide technical and financial assistance for the environmentally sound disposal of obsolete pesticides. The following considerations may give justification for providing such assistance:

   Nevertheless, even though aid agencies may be prepared to assist countries with a one-time intervention to dispose of old stocks, it is unlikely that they will be prepared to support the same countries in any subsequent disposal activities. Developing countries and aid agencies should therefore take the necessary precautions to ensure that present and future stocks of pesticides do not become obsolete.


1 The following three conventions are based on the UN's Recommendations on the transport of dangerous goods, which cover principles of classification, general packaging requirements, testing procedures, marking, labelling or placarding, and shipping documents: The International Convention for the Prevention of Pollution from Ships (MARPOL) and the accompanying International Maritime Dangerous Goods (IMDG) Code, which provides standards for the shipment of dangerous goods by sea; The Convention on International Civic Aviation (Chicago Convention) and the accompanying Technical Instructions for the Safe Transport of Dangerous Goods by Air; The Convention concerning International Carriage by Rail. Go back
2 At the time of publication of these guidelines, 18 African countries had submitted completed inventories. Extrapolation of the figures from these countries provides an overall estimate for Africa of 15,000-20,000 tonnes of obsolete pesticides (excluding heavily contaminated soils). Go back
3 Many of the older types of cement kilns are not suitable. Only a few of the cement kilns in developing countries meet the technical requirements that, in principle, would make them suitable for incineration of certain groups of pesticides. Expert advice is needed to assess whether kilns can be used and special equipment is required to inject the pesticides into the kiln. Such equipment is expensive and should only be installed and used under expert supervision. The use of mobile incinerators requires advanced road infrastructure, reliable and continuous supplies (fuel, electricity and chemicals) and expert supervision. In most cases, the use of mobile incinerators is unlikely to be cost-effective for quantities of fewer than 1,000 tonnes. Go back

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