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Persistent Toxic Substances and “Persistent Organic Pollutants”

Substances in this category are diverse. They include substances that are persistent in the sense of being long-lived and relatively slow to breakdown into other less persistent chemicals. They also include less persistent chemicals that, because of the amounts in widespread and continuing use, occur in significant equilibrium concentrations in the environment and are of concern due to possible adverse effects.

There is currently a Global Environment Facility (GEF)-funded evaluation of so-called "persistent toxic substances" (PTS) which includes attention to some less persistent substances that, because of their continuing use and dissemination, may give rise to chronic exposures over large temporal and spatial scales.

The so-called Persistent Organic Pollutants or "POPs" that are the main focus of current international negotiations leading to a global agreement also reside in this category. They are characterized by low solubility in water and high solubility in lipids. They are stable to photochemical, chemical and biological decomposition, and therefore accumulate in fatty tissues. Due to their volatility, several of these substances can undergo long-range atmospheric transport and deposition to the ocean. Most POPs of contemporary concern in the marine environment are synthetic compounds produced for the benefit of society, but their beneficial features must be weighed against their negative effects on human health and the environment.

Included in this group of 12 substances are polychlorinated dibenzo-p-dioxins (PCDD) (often simply referred to as "dioxins") and polychlorinated dibenzo-furans (PCDF) (often simply referred to as "furans"). These are discharged into water, largely from pulp mills using chlorine as a bleaching agent and certain types of treated wood feedstock, and give rise to predominantly local effects through, for example, the contamination of seafood. Larger-scale concerns are associated with PCDD and PCDF releases to the atmosphere from waste combustion. These compounds are, however, not purely artificial and are also produced in natural forest fires.

International controls on the production and use of a small number of POPs were introduced more than 20 years ago. Indeed the atmospheric concentrations of the controlled substances have decreased in remote areas of the northern hemisphere, showing that action can be effective.

However, even where the use of some POPs has been discontinued, many developing countries lack the capacity to dispose of remaining stockpiles.

Controls on POPs currently address only a small fraction of the potentially dangerous chemicals and there are persuasive arguments for broader international controls on the production and release of chemicals with physical-chemical properties known to be inimical to the environment.

The increased use of these substances in areas of the world where regulations are not in place, or not enforced, represents a serious challenge – as do the threats posed by new substances coming into commercial use. Several major international efforts have been devoted to the integrated assessment of the primary inventories and pathways of certain POPs. These efforts have been useful, but obviously they are only a small part of what will be needed in both the near and the distant future.

 

Source: GESAMP71:21