11. Health Risks Associated with Organic Pollutants in Soils

The occurrence of organic pollutants at elevated levels has been of significant environmental and human health concern at numerous contaminated “hot spots” and their regional and global importance has received increasing attention in the last decade. Many different forms of organic pollutants exist. Among this group, persistent organic pollutants (POPs) play a key role. Importantly, POPs have the ability to enter the gas phase under environmental temperatures and may volatilize from soils, vegetation and water bodies into the atmosphere. Because of their resistance to breakdown reactions in the air they travel long distances before being re-deposited. The cycle of volatilization and deposition may be repeated several times, with the result that POPs could accumulate in an area far away from where they were used or emitted.

POPs are either intentionally produced for one or multiple purposes, or they are unintentionally formed as by-products in other processes. Minor quantities Polybrominated Diphenyl Ethersmay also result from natural processes. Several pesticides (Chap. 10), industrial chemicals and unintentionally formed substances are commonly mentioned in the context of POPs. This chapter focuses on industrial and unintentionally formed substances. The processes leading to unintentional production of POPs can be categorized as combustion and chemical-industrial processes. Some important examples are the emissions of dioxins (e.g. polychlorinated dibenzo-p-dioxins: PCDDs), furans (e.g. polychlorinated dibenzofurans: PCDFs) and polycyclic aromatic hydrocarbons (PAHs). Several POPs belong to various source categories, e.g. polychlorinated biphenyls (PCBs) that have been produced as an industrial chemical, but can also be unintentionally formed in combustion processes.

Persistent organic pollutants are toxic and resist to photolytic, biological and chemical degradation to varying degree. Persistent organic pollutants are also known to be semi-volatile, which permits these substances to occur either in the vapor phase or adsorbed on particles in the atmosphere. This enables their long-distance transport through the atmosphere. The persistence in combination with semi-volatility has resulted in worldwide, nonpoint source pollution of soils and ecosystems with organic pollutants. They occur even in remote regions including open oceans, deserts and poles where no local sources are present. Dumping of POPs in badly engineered and unsuitable landfill sites and dumps has often caused point source pollution around these sites with widespread contamination of groundwater and surface water contamination particularly from hexachlorocyclohexane (HCH), hexachlorobenzene (HCB) and PCB.

Due to their bio-accumulating properties these substances build up in the food chain with exposure to animals and humans, possibly causing health impacts for current and future generations. Because of their harmful effects on man and wildlife, international agreements have come into effect to reduce future environmental risks. Persistent organic pollutants have been globally addressed by the Stockholm Convention which was enacted in 2004. This convention aims at protecting environmental and human health from adverse effects associated with exposure to POPs. Twelve of these POPs were originally listed but the number is increasing with nine new POPs added in 2009. While the original emphasis of the Stockholm Convention was on chlorinated compounds such as PCBs, HCBs, polychlorinated dibenzo-p-dioxins, dibenzofurans, POP pesticides and some others, fluorinated and brominated POPs were added to the convention in 2009. The latter include polybrominated biphenyls (PBBs) and polybrominated diphenyl ethers (PBDEs) which have been widely used as flame retardants for electronics, textiles, furniture, upholstery, insulation foam, etc. The first fluorinated additions to the Convention were perfluorooctane sulfonic acid (PFOS) together with its salts. PFOS and related compounds are increasingly entering waste streams in a wide range of products. Polychlorinated naphthalenes (PCNs) are under review by the Stockholm Convention as a candidate for POPs for their persistence, toxicity, bioaccumulation, and long-range atmospheric transport. Like other POPs, PCNs are globally distributed in air, sediments and biota. Short-chain chlorinated paraffins (SCCPs) are also found worldwide in the environment, and are bioaccumulative in wildlife and humans.

Organic pollutants are strongly linked to human health effects such as cancers, mesothelioma, skin disorders, respiratory diseases, eye disorders, asthma and endocrine disruption. Humans can be exposed to POPs through direct exposure, occupational accidents and the environment. Short-term exposures to high concentrations of POPs may result in illness and death. Chronic exposure may be associated with a wide range of adverse health and environmental effects.