1. Obsolete Pesticides – A Threat to Environment, Biodiversity and Human Health

Since Rachel Carson’s passionate warning in the seminal 1962 book ‘Silent Spring’, which is now celebrating 50 years from its publication, concern on the steadily increasing accumulation in the environment of chemically robust, biologically persistent and possibly toxic organochlorine pesticides led to their substitution with less threatening products and finally to stop or limit their production and to severely restrict their use. In particular, the Stockholm Convention on Persistent Organic Pollutants (POPS) signed in 2001 banned or greatly restricted 12 chlorinated organic compounds or classes due to their toxicity and ability to accumulate in the environment and to magnify through the global trophic network. Among them are 11 pesticides namely aldrin, chlordane, DDT, dieldrin, endrin, heptachlor, hexachloro-benzene, kepone, lindane, mirex, toxaphene. These pesticides played a historical role in mitigating the health impact of parasite-borne human pathogens such as malaria parasites and in protecting food crops to allow better feeding of an increasingly raising population especially in sub-tropical and tropical areas. Concern for human and environmental health is mainly due to long-term effects of some substances, in particular through endocrine disruption, interference with reproduction, carcinogenicity, although the actual size of effects of real-life exposure is still an active and debated research topic. Risk assessment and risk-benefit analysis of some key pesticides such as DDT still need a thorough understanding of the toxicity mechanisms and of its relevance to humans in the different life-stages. As a consequence of the Stockholm ban, large stockpiles of unusable pesticides accumulate in some countries and thus present considerable threat to the environment and to human health, also due to unavoidable degradation of the active formulated substances into poorly tractable materials. To avoid environmental damage through contamination of water and agricultural land resources by leaching or improper disposal of repositories, inventories of existing stockpiles are needed to plan and carry adequately safe disposal interventions. Methods for disposal need to tackle the peculiar chemical characteristics of these highly chlorinated aliphatic and aromatic compounds, i.e., very low water solubility and an unusual stability towards acid, basic and oxidizing conditions. Research and technology development in this field is currently exploiting the most advanced ‘green chemistry’ approaches, aimed at an as complete mineralization of organo-chlorine substrates with as negligible production of toxic waste. We will draw a brief historical perspective of the genesis of this pivotal environmental problem, review the use of the ‘dirty dozen’ pesticides and their contribution to the Green Revolution improvement of agricultural food availability, the ecotoxicological and human health concern and the current efforts to front the problems raised by their use.