Persistent Organic Pollutants (POPs) are chemical substances that persist in the environment, bioaccumulate through the food web, and pose a risk of causing adverse effects to human health and the environment (UN Environment Programme). In the Asian and Pacific (ASPAC) region, the residues of pesticides and POPs are widely distributed in soil, water, air, living creatures, and crops. POPs such as pesticide chlorinated hydrocarbons (e.g. DDT, drins: aldrin, dieldrin, endrin, etc.), dioxins, and polychlorinated biphenyls (PCBs) are very resistant to natural (biological, chemical and physical) decomposition in the environments, and persistently remain in the soil for decades.
With recent advances in analytical technology, the distribution and dynamics of POPs and ordinary pesticides in the environments can now be traced at their pico- and even nano-levels. Consequently, some POPs have been identified as present in crop produce such as vegetables, fruits, tea leaves, etc. The POPs found in these crops are likely to have been derived from soil, water and air. However, among these three POPs sources, contaminated soil is the most important source. Various pollutants such as POPs and ordinary pesticides are brought intentionally and unintentionally into the soil, and have accumulated through the years. These persistent pollutants remain in the soil for a long time, some of which gradually decompose and are absorbed by the crops, and eventually flow out of the arable land to the surrounding environments.
With the evidence of long-range transport of these substances to regions where they have never been used or produced and the consequent threats they pose to the environment of the whole globe, the international community has now, at several occasions called for urgent global actions to reduce and eliminate releases of these chemicals. The Stockholm Convention on POPs requires participating parties to develop their respective National Implementation Plan (NIP) to reduce or eliminate releases from unintentional production of POPs, as well as releases from stockpiles and wastes with POPs, for the protection of human health and the environment.
Hence, in 2002, in accordance with the Stockholm Convention, the workshop on “Environment monitoring of POPs in east Asian countries” was held with the participation of 10 Asian countries namely, Cambodia, China, Indonesia, Japan, Korea, Malaysia, Philippines, Singapore, Thailand and Vietnam. The OECD has likewise proposed a new Chemical Pesticide Guidelines to help member countries in assessing and reducing pesticide risks to human health and the environment. Recently, Japan complied with the new guidelines by drastically revising its Registration of Chemical Pesticide Regulations based upon the concept of “Positive Listing System of Chemical Pesticides.” After enforcement of this new registration guideline, the public has become more aware of the need to be vigilant against the increasing presence of pesticide residues in foods. People are now giving more attention to safe foods cultivated with less/no pesticide use, hence, less pesticide residue.
However, under intensive farming common in Asian small-scale farmers, pesticide spray to the targeted crops also affects other crops and vise versa. Several short-duration crops are planted not far apart from each other on the same plot. Similarly, relay cropping with short-duration crops is common in vegetable production, particularly under protected cultivation. For such mixed culture and relay cropping, pesticides sprayed to the targeted crops can affect not only other crops on the same plot, but also the succeeding crops due to the short time interval. The pesticides applied to the preceding crops cannot be completely decomposed within the Plant Harvest Interval (PHI), and some are left over in soil, and possibly taken-up by the succeeding crops. Thus, the problem of pesticide-residue is closely associated with cropping systems adopted in the region, and this will be more serious for Asian small-scale farmers adopting more intensive/complicated cropping systems under the year-round production.
This international seminar aims to promote a better understanding of the current status of POPs distribution in the environments, particularly in arable soils in the ASPAC region, and to discuss the adverse effects of POPs on food safety based on recent and advanced studies in this region. In addition, standards and appropriate use of chemical pesticides in the context of IPM systems will be discussed and recommended for Asian small-scale farmers under intensive farming with short-duration crops such as vegetables and specialty tuber crops.