Volume 68, Issue 9

Chlorine, in the form of its salts, has been known since the earliest days of recorded history, although its recognition as an element did not occur until the beginning of the nineteenth century when its very high reactivity as an oxidant was found remarkable after it was shown not to contain any oxygen. Its absorption by sunlight made it a key substance in the early development of photochemistry. One example of this, with both pure and applied aspects, is described in more detail. The free radical chloric oxide played an important role in the development of the technique of flash photolysis and twenty five years later these researches were of essential importance in showing how chlorine and its oxides were involved in the destruction of the ozone layer by the chlorofluorocarbons.

Earth's chlorine, retained when the planet was formed from the Solar nebula, is contained largely in three reservoirs: the mantle (99.6%), the crust (0.3%), and the oceans (0.1%). Only oceanic chlorine is readily mobile, cycling among the lower and middle atmosphere, the pedosphere, freshwaters, and the cryosphere. Inter-reservoir chlorine fluxes are estimated for all transitions of interest; by far the most important on a mass basis is the injection of seasalt from the oceans to the atmosphere, and its return to the planetary surface by wet and dry deposition.

Of the more than 2,600 known naturally occurring organohalogen compounds, more than 1,500 contain chlorine. These organochlorines, which range in structural intricacy from the ubiquitous fungal and plant metabolite chloromethane to the complex life-saving antibiotic vancomycin, are produced by marine and terrestrial plants, bacteria, fungi, lichens, insects, marine animals (sponges, sea hares, nudibranchs, gorgonians, tunicates), some higher animals, and a few mammals. New examples are continually being discovered and the total number of natural organohalogens may surpass 3,000 by the turn of the century.

Numerous products, such as polymers, chemicals or pharmaceuticals and ultra-pure metals, which often do not actually contain chlorine, are produced using either chlorine or its derivatives. They are essential in all industrial sectors and in our daily lives. New chlorine production units have adopted the membrane electrolytic process, but the century-old diaphragm and mercury processes retain their high-performance characteristics when appropriately modernised and improved.

The pulp and paper industry in Canada contributes significant effluent discharges to surface and marine waters. Chlorine and chlorine compounds are used in the bleaching of pulp. A large number of organochlorine chemicals of widely differing properties are, or have been, produced from this bleaching. These range from the highly hydrophobic, persistent and bioaccumulative toxic substances, such as 2,3,7,8-TCDD, to the higher molecular weight, non-hydrophobic material usually characterized by absorbable organic halogen. Chlorine dioxide and chlorine react with lignin by different chemical processes and produce different organochlorine products. Use of molecular chlorine as a bleaching agent results in the formation and release of chlorinated organic compounds, sometimes at concentrations that present an unacceptable risk to the receiving environment and the food chain. Alternatives to the use of molecular chlorine, such as chlorine dioxide, result in reductions in the quantities of organochlorines produced, and the degree of chlorine substitution in the organochlorines formed. This, in turn, leads to reduced persistence, reduced potential for bioaccumulation and food chain transfer, reduced toxicity and reductions in adverse ecological effects. However, sufficient evidence exists from responses observed at non-bleached mills to show that other (probably non-halogenated) compounds are released or formed during the production of pulp and cause responses such as induction of MFOs, changes in hormone levels, and reproductive effects.

Disinfection of drinking-water is one of the main achievements of our time in the protection of public health. The use of chlorine for the destruction of microbiological pathogens is essential to protect the public from outbreaks of waterborne disease. Chlorine, as well as other disinfectants, produces a variety of chemical by-products. The risk from the presence of microbial pathogens in drinking-water is estimated to be several orders of magnitude greater than the risk from chlorination by-products. Any efforts to control these by-products must not compromise the microbiological quality of drinking-water.

The environmental behavior of a chemical is governed by its intrinsic physicochemical properties, including their metabolic activities, as well as by characteristic features of the environmental compartments. This inextricable network of interactions contribute to degradation and mineralization of organic compounds. Under the circumstances that the chemical is lipophilic and/or resistant against chemical and biological degradation, it tends to be transported to other environmental compartments and/or subject to bioaccumulation. The adverse effects of chemicals on humans and organisms in the environment are assessed by a variety of toxicological studies to establish ADI (acceptable daily intake in man) or PNEC (predicted no observed effect level in organisms), in comparison with the calculated exposure levels based on the environmental behavior of chemicals.

The chlorofluorocarbons (CFCs) are industrialchemicals used as solvents, refrigerants, plastic foam blowing agents,etc. These compounds are eventually released to the environment; theyslowly drift into the stratosphere, where they decompose, initiatinga catalytic process involving chlorine free radicals and leading toozone destruction. The stratospheric ozone layer is important for theearth's energy budget, and it shields the surface of the earth fromultraviolet radiation from the sun. Very significant depletion of theozone layer has been observed in the spring months over Antarctica duringthe last 10-15 years. Laboratory experiments, model calculations andfield measurements, which include several aircraft expeditions, haveyielded a wealth of information which clearly points to the CFCs asthe main cause of this depletion.

A very considerable body of data pertaining to the atmospheric behaviour of hydrochlorofluorocarbons (HCFCs) and chlorinated solvents is now available and leads to the following conclusions: (a) these compounds, with the exception of 1,1,1-trichloroethane, make a small or insignificant contribution to stratospheric ozone depletion, global warming, "photo-chemical smog", "acid rain", or chloride and fluoride levels in precipitation; (b) it seems highly unlikely that the chlorinated solvents degrade in the atmosphere to give chloroacetic acids as major products, as has often been claimed in the literature.

The relationship between physicochemical properties, environmental distribution and effects of organochlorine compounds as a major class of persistent organic pollutants (POPs) are discussed. The environmental fate of a compound includes its transport and dispersion in the environment as well as its accumulation and transformation in defined environmental compartments. Accumulation and transformation as the result of environmental distribution may have long-term consequences; this is indicated by the ultimate accumulation and long-term bioactivity of several widely spread organochlorines, and is clearly evident in the decomposition of chlorofluorocarbons in the stratosphere. Depending on the order of trophic levelsbiomagnifiaction factors of 10,000 up to 100,000 are encountered for persistentsemivolatile organochlorines such as 4,4'-DDE, PCB congeners or some Toxapheneconstituents. Mammals show intra-species pollutant transfer during thelactation period. While the mother animal is partly depleting its bodyburden, the calve accumulates in a critical period of its life via themilk a concentrated input of persistent organochlorines. A similar depletionphenomenon is also found for fish and crustacean which enrich in the eggsa substantial part of the accumulated body burden of the female. The air skimming of semivolatiles by plantsurfaces leads to surprisingly high levels of pollutants in the uppersoil layers of forests that otherwise would be considered pristine interms of human activities.

Polychlorinated dioxins and dibenzofurans are two series of tricyclic aromatic compounds, which have been the focus of the interest in the last decades; in all there exist more than 200 congeners. They are formed in numerous ways, primarily in incineration processes and in industrial processes. It has also been found that they are formed by natural processes. They are ubiquitous and have been quantified in abiotic samples such as soil, sediments and air as well as in living organisms, primarily aquatic organisms. A dramatic decrease in most environmental concentrations including biological and human samples of PCDDs and PCDFs has been identified. There is a discrepancy between sources and environmental reservoirs which cannot be fully explained.

The chlorinated organic compounds comprise a large group of compounds with a complex diversity of biologic effects and mechanisms of action. Based on the persistence and high toxicity of dioxins, PCBs, and DDT, this chapter focuses primarily on the toxicology of these organochlorine compounds. Not even these groups of compounds can be regarded as homogenous since the individual congeners show diverse environmental fates and toxicities. In this chapter, we will consider primarily the critical effects suspected to occur at human exposure at background levels, i.e. cancer, and effects on reproduction, neurobehaviour and the immune system. In recent years, interactions between these compounds and hormonal systems have received increasing attention. They have also been shown to be particularly toxic to the developing embryo, fetus and infant. In order to conduct accurate risk assessment, there is a need for further mechanistical data, and additional epidemiological studies, especially with regard to effects on reproductive, neurobehavioural and immune systems. The data presently available suggest that such effects already occur in the human population and thus, in order to reduce the exposure to these compounds, further release into the environment should be prevented.

Sound environmental management includes the proper management of waste. This chapter reviews the basic rules of good management practice illustrated by some examples from chlorine derivatives production and gives the main considerations governing the Best Available Techniques for organochlorine waste thermal treatment. A review of the main degradation pathways of organochlorines - dispersal, distribution, degradation pathways, and environmental half-lives - demonstrates a very large range of characteristics, justifying the need for a separate study for each substance. Finally, the paper examines the latest developments in organochlorine contaminated site remediation technology.

PVC is the second most important polymer worldwide. Thanks to its excellent cost/performance ratio and outstanding chemical and environmental resistance, it is today mainly used for long-life applications. In some countries, for example, France, PVC is used in large volume for the manufacture of bottles. Pure PVC scrap can be recycled without any problems. Although many applications for such products of recycled PVC have been developed, and pilot plants for recycling exist, only small volumes have been recycled up to now. Only bottles made from PVC for the large drinking water market in France are already collected separately, recycled in large quantities, and transformed into such articles as water pipes. Specialist organisations deal with this business. In such cases, for example, kitchen waste, where PVC is part of mixed plastics waste for example, sorting and separation of the PVC is necessary.

A crusade is ongoing against element 17 in the periodic table, i.e. chlorine, one of the most abundant on earth. It is blamed, amongst other things, to be responsible for the depletion of the ozone layer, bioaccumulation of chlorinated compounds such as DDT or PCB's in animals and for the formation of dioxins in urban waste incineration. Due to socio-economic implications the issue has gone too early beyond the borders of the scientific community, before facts have been proven and evaluated. As a result, it has been treated in inappropriate and emotional ways even affecting scientific ethics in some cases. Therefore, the International Union of Pureand Applied Chemistry (IUPAC), conscious of its responsibilities in thisarea, has decided to publish this White Book with the collaboration ofoutstanding worldwide renowned scientific specialists from North-America,Europe and Japan in order to inform the public and the decision makersas well as the scientific community in an objective, open and unbiasedway on the up-to-date scientific knowledge. In doing so IUPAC is following its philosophyto make independent judgments on important issues that are touchy or sensitiveto the general public, governments and industry. IUPAC is not acting asa judge, but would like to critically evaluate the various factors forand against a particular issue. The occurrence of chlorine in nature andalso in living organisms, either as inorganic compounds or as numerousand very diversified natural "organo-chlorines" does not makeany doubt any more (T. GRAEDEL and W.C. KEENE, G.W. GRIBBLE). The availability of the raw material, salt,the development of convenient production technologies and the chemicalproperties of chlorine have generated a blooming tree of applicationsin such different fields as the pulp and paper industry (K. SOLOMON),the disinfection of water (H. GALAL-GORCHEV) but mainly in organic synthesisleading to a host of useful products, for example, polymers, pharmaceuticals,pesticides, dyes and pigments (J. FAUVARQUE). It is quite clear that chemists have notalways been aware beforehand of all the possible consequences of havingmanufactured new molecules, be they chlorinated or not. Chemicals emittedvoluntarily or inadvertently in the environment are distributed thereaccording to a complex set of physico-chemical properties (J. MIYAMOTO, K. BALLSCHMITER). Volatile compounds such as aliphatic chlorinatedand chlorofluorinated hydrocarbons find their way to the "atmosphericcompartments". Long-lived members of this family are even able toreach the stratosphere where they have been shown to produce detrimentaleffects to the global environment (M. MOLINA). The substitution of these so-called CFC'sby new shorter-lived molecules has probably been the best example of asound scientific approach to solving environmental problems. A host ofscientific studies has shown that short-lived chlorinated aliphatic compoundsmake only minor or even insignificant contributions to environmental problemssuch as stratospheric ozone depletion, global warming, "photochemicalsmog", "acid rain" or chloride levels in precipitations(J.A. FRANKLIN and H.W. SIDEBOTTOM). Are organo-chlorines harmless or harmful? The question seems as irrelevant as asking if natural compounds areharmless and anthropogenic ones toxic. Ecotoxicity (K. BALLSCHMITER) and toxicity(A. HANBERG) as any other "chemical" property of any compounddepends on the structure of its molecule; chlorinated or otherwise halogenatedcompounds do not escape this rule. Therefore, an undifferentiated banof whole classes of chemical compounds has to be qualified as unscientific. Even in apparently "homogeneous"families such as the dioxins, toxicity varies considerably with the positionand the number of substituents (Ch. RAPPE). There is thus no scientificfoundation to the amalgamation of all chlorinated compounds as a groupshowing special toxic and ecotoxic properties, no more than one shouldconsider organo-oxygens or organo-nitrogens as a whole as harmful becausehighly toxic warfare agents as sarin or tabun contain these atoms in theirmolecules. This obviously doesn't mean that organo-chlorinewaste, as any sort of waste, has not to be managed. The problem has beentackled and technical solutions have been developed to reduce byproductsformation by improving the production processes, to destroy and/or valorisethe remaining production wastes (R. PAPP). This has now to be generalizedin the most economic and environmentally friendly ways. In some cases,post-use recycling is being developed and starts to be generalized asfor the recycling of PVC for which "second life" applicationshave been found (G. MENGES). In conclusion, I would like to add a fewwords formulated by the Nobel laureate Prof. Lord George Porter earlieron. "There is no way that humans can foresee all the consequencesof their actions, .... The only sure foundation for security in this technologicalworld is to have a science base which is continually asking whatever questionsseem interesting and is always there to advise and to act when the needemerges." It is the responsibility of the scientificcommunity to develop this science base, of the media to help them toinform the public in an understandable and unbiased way, of the publicauthority to take the relevant decisions on the bases of sound scienceand not on emotional reactions and of industry to act responsibly, endorsingproduct stewardship and responsible care. This is true for chlorineand its chemistry as well as it is for all human activities.