Since many commercially important bulk chemicals are volatile, their eventual degradation, mostly by photochemical reactions, is a critical factor for the pollution and environmental hazards so caused.
This compilation on the breakdown of 1,100 commercially important chemical products is the first publication to make this knowledge publicly accessible in one book. The data and annotations have been painstakingly assembled over a 10-year period in a cooperation among academia and regulatory authorities. It explains in detail the methods, including computational ones, for the environmental assessment of volatile and semi-volatile substances, and is rounded off with data tables of degradation rates.
From the contents:
* Photodegradation
* Heterogeneous degradation
* Experimental determination
* Environmental relevance
* Data tables of degradation rates
A key resource for manufacturers and regulators of such substances.

Prof. Dr. Walter Klopffer studied chemistry at the Karl-Franzens-University in Graz, Austria. He then joined the Battelle Institute in Frankfurt/Main, Germany, and since 1975 he is also Professor for Physical Chemistry at the University of Mainz.
Dr. Klopffer’s main fields of interest include the spectroscopy and photophysics of aromatic polymers, and the environmental assessment of chemicals (persistence, abiotic degradation) and products (Life Cycle Assessment).

Dr. Burkhard Wagner obtained a PhD in Chemistry from the University of Heidelberg, Germany. He completed a postdoctoral period at the California Institute of Technology with George Hammond before joining the German Federal Environmental Agency (Umweltbundesamt), where he was the long-time section head for environmental impact assessment of chemicals.

Prof. Dr. Walter Klopffer studied chemistry at the Karl-Franzens-University in Graz, Austria. He then joined the Battelle Institute in Frankfurt/Main, Germany, and since 1975 he is also Professor for Physical Chemistry at the University of Mainz.
Dr. Kloepffer’s main field of interest is the spectroscopy and photophysics of aromatic compounds, and the environmental assessment of chemicals.

Dr. Burkhard Wagner obtained a PhD in Chemistry from the University of Heidelberg, Germany. He completed a postdoctoral period at the California Institute of Technology with George Hammond before joining the German Federal Environmental Agency (Umweltbundesamt), where he was the long-time section head for environmental impact assessment of chemicals.

Atmospheric Degradation of Organic Substances

By Walter Klöpffer Burkhard O. Wagner Klaus Günter Steinhäuser

John Wiley & Sons

Copyright © 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
All right reserved.
ISBN: 978-3-527-31606-9

Chapter One

Significance of Photo-degradation in Environmental Risk Assessment

1 Introduction

Photo-degradation (or transformation) occurs under the influence of solar radiation mainly in the atmosphere, and to a lesser extent in the hydrosphere and on soil surfaces. New developments in environmental risk assessment have given photo-degradation new significance, which will be described in this introduction. The data collected in this book refer to gas-phase photo-degradation in the atmosphere, and so does this introduction. Photo degradability is an intrinsic property of a chemical substance and must be measured. Quantitative structure activity relationships (QSARs) for estimating gas-phase rate constants of the indirect photo-degradation of organic chemicals are available and will be discussed in Section 5. Reactive species, which degrade a chemical substance in the atmosphere, are the hydroxyl radical, ozone and the nitrate radical. As these species are produced via solar radiation, this mechanism of degradation is known as “indirect”, in order to distinguish it from the direct photolysis by solar radiation.

Photochemistry is a discipline within physical chemistry, and more specifically, atmospheric chemistry that is dealt with in the text books by Finlayson-Pitts and Pitts. Photo-degradation of organic substances is the subject of Chapter 2. The subject of interest to environmental chemists and administrators is the capacity of solar radiation to degrade, destroy and finally eliminate man-made chemical substances from the atmosphere. Atmospheric distribution of a chemical substance is critical because it can potentially lead to world-wide dissemination, if it is long-lived (persistent) and not destroyed. If this elimination mechanism did not occur, mankind would have suffered from severe air pollution and respiratory health problems, which are still the case in urban agglomerations as a result of air pollution, where the atmospheric elimination processes are not sufficiently efficient.

In the early 1980s Atkinson and Becker et al. began the systematic testing of volatile organic substances on gas-phase photo-degradation with the hydroxyl radical. At the time that the regulation of chemicals was drawn up, “photo-degradation” under the term of “abiotic degradation” was not considered important. Photo-degradation was not part of the OECD pre-minimum set of data in the assessment of chemicals, which was the example for the European legislation in the 6th Amendment of the 67/548/EEC Directive (1979).

This book, with the data collected in it, underlines the role of photo degradability as one of the important intrinsic properties that steers the atmospheric fate of chemicals and thereby contributes to “persistence” and “long-range transport potential”. With the acceptance of multimedia environmental fate models in legal exposure assessment, photo degradability underwent a renaissance of importance as shown below.

2 Persistence and Long-range Transport Potential in Chemicals Regulation

Environmental persistence of organic substances was heralded by two publications that shook the scientific community as well as the politicians: Rachel Carson’s Silent Spring in 1962, and the discovery by Rowland and Molina in 1975 that fluorochlorocarbons are stable (persistent) molecules in the troposphere (the lower 10 to 15 km of the atmosphere) and may deplete the ozone in the next layer of the atmosphere, the stratosphere. Persistence implies the absence of chemical, biological and physical degradation processes in the environment so that organic molecules, once emitted from the technosphere by anthropogenic activity, remain, distribute and accumulate in the worldwide environment. Persistence is an environmental (negative) term and should be distinguished from the (positive) term “durability” of a chemical product during use. In the following we will draw attention to the interaction between the scientific and the administrative communities with respect to the slow change in perception of the term “persistence”.

“Persistence” first surfaced in the OECD in 1966, when the OECD Committee for Scientific Research held a conference on “Research on the Unintended Occurrence of Pesticides in the Environment”. At that time the OECD established a study group on this problem, and its report led, in 1971, to the creation of the OECD Environment Committee with the following recommendations:

“The Group wishes to stress the need internationally for means to make comprehensive investigations of the consequences of use, and limitations in use, of those chemicals which could be regarded as having unacceptable effects on man and his environment resulting from, either

a) their undue persistence in natural conditions in biologically active form, or

b) their wide distribution through water and air, or

c) their accumulation which may lead to biological effective levels in organisms exposed to even low concentrations.” [8, p. 11]

At the same time the United Nations Conference on the Human Environment (1972) recognised persistence as a negative environmental property in Recommendation 71:

“It is recommended that Governments use the best practical means available to minimize the release to the environment of toxic or dangerous substances, especially if they are persistent substances such as heavy metals and organochlorine compounds, until it has been demonstrated that their release will not give rise to unacceptable risks or unless their use is essential to human health or food production, in which case appropriate control measures should be applied.”

These two recommendations have not changed with the years and read like a contemporary political mandate. However, the environmental regulatory discussion treated “persistence” only as a sub-element of environmental effects assessment, and it took several years and arguments before “persistence” was accepted as an environmental criterion in its own right and designated as an “endpoint” in environmental exposure assessment equivalent to “ecotoxicity”. In 1977 Stephenson foresaw the future problem of persistent chemicals, when he wrote:

“Persistent materials, because of this property, will accumulate in the environment for as long as they are released. Since the environment is not effective at cleansing itself of these materials, they will remain for indefinite periods, which were not recognized at the time of their original release. The problem could become entirely out of control and it would be extremely difficult if not impossible to do anything about it. Materials which are strongly persistent can accumulate to rather high levels in the environment and effects which would not otherwise be important could become so.” [10, p. 48]

Frische et al. (1982) [11] and Klöpffer (1994) [12, 13] advocated that “persistence” is the “central and most important environmental criterion” often replacing ecotoxicity, which can never be determined with acceptable certainty.

At the beginning of the 1990s, semi-volatile organic chemicals (SOCs) came into focus for analytical chemists because of the worldwide distribution, ubiquitous occurrence and geo accumulation in remote areas (Ballschmiter and Wittlinger, Ballschmiter, Ockenden et al., and AMAP). This was a disturbing signal for sustainable chemical production and use, and alarmed the regulatory community, after “sustainable development” had been established as the key policy environmental term at the Earth Summit in Rio de Janeiro in 1992. In fact, Agenda 21 formulated the future chemicals risk assessment policy, by including:

“Governments, through the cooperation of relevant international organisations and industry, where appropriate, should adopt policies and regulatory and non-regulatory measures to identify, and minimize exposure to toxic chemicals by replacing them with less toxic substitutes and ultimately phasing out the chemicals that pose unreasonable and otherwise unmanageable risk to humans and the environment and those that are toxic, persistent and bio-accumulative and whose use cannot be adequately controlled.” [18, Chap. 19.49 (c)]

Another milestone in this policy discussion was the Esbjerg Declaration, which nine European countries neighbouring the North Sea and the European Commission adopted in Esbjerg, Denmark, 8th–9th June 1995, at the Fourth International Conference on the Protection of the North Sea. The statement of zero concentrations for man-made synthetic substances in the North Sea was revolutionary and was received with scepticism, but did not miss its policy objective.

17. The Ministers AGREE that the objective is to ensure a sustainable, sound and healthy North Sea ecosystem. The guiding principle for achieving this objective is the precautionary principle.

This implies the prevention of the pollution of the North Sea by continuously reducing discharges, emissions and losses of hazardous substances thereby moving towards the target of their cessation within one generation (25 years) with the ultimate aim of concentrations in the environment near background values for naturally occurring substances and close to zero concentrations for man-made synthetic substances. Esbjerg Declaration 1995.

In 1997 the Chemicals Policy Committee of the Swedish Ministry of the Environment outlined specific sustainability goals: “Substances that are persistent and liable to bioaccumulation should be banned, even if they are not known to have toxic effects.” The Committee argued:

“Experience tells us, that new unexpected forms of toxicity may be uncovered in the future. For substances that are persistent and liable to bioaccumulate that knowledge will come too late. To act only when the knowledge of the hazard becomes available is not prevention. We therefore conclude that known or suspected toxicity is not a necessary criterion for measures against organic man-made substances that are persistent and liable to bioaccumulate. Such substances should in the future not be used at all.”

One year later Martin Scheringer et al., [22, Chap. 1–3], [23, Chap. 1–3] advocated a change in the paradigm of environmental risk assessment, in short a shift from the effects-based to the exposure-based assessment. Scheringer and Berg had prepared this change by introducing the following three indicators for measuring environmental threat:

• spatial range (potential for long-range transport)

• temporal range (persistence)

• bioaccumulation potential

Scheringer and Hungerbhler [26, p. 176] concluded:

“An exposure-based assessment requires different (and usually less) data than effect-based assessments and is (usually) performed faster than the various toxicity tests required for an effect-based assessment.

It should be noted that the combination of persistence and bioaccumulation, although relevant for many semi-volatile organic substances, is “narrower” than the concepts of Klöpffer and Scheringer and would not include, for example, new types of freons contributing to global warming or other, hitherto not recognized effects. The same is true for persistent water-soluble substances and thus not bioaccumulating substances.

Subsequently, in 2001, the German Umweltbundesamt and Steinhuser argued similarly, when they published five policy principles on sustainability, two of which are concerned with persistence:

• “The irreversible release of persistent and bioaccumulative or persistent and highly mobile pollutants (xenobiota) in the environment must totally be avoided regardless of their toxicity. This also holds for metabolites with the same properties.

• The increase of releases must be avoided independently of known adverse effects and other intrinsic properties, if it is practically impossible to recollect the substance from the environment because of its high mobility and/or its significant partitioning.” [27, pp. 78]

In Canada, indigenous people, such as the Inuit, complained that they were not users of persistent chemicals, but suffered from the air-borne fallout and the contamination of their grounds living in the Arctic.

Important milestones in this policy discussion on persistence were the 1985 Vienna Convention for the Protection of the Ozone Layer and the Montreal Protocol on Substances that deplete the Ozone Layer. This Convention and its Protocol triggered off an intensive research on the gas-phase photo-degradation and the global warming potential of hydrofluorocarbons (HFCs), hydrofluoroethers (HFEs) and polyfluoroethers, because such fluorated chemicals have valuable uses and are of high economic interest.

“Persistence,” “bioaccumulation” and “long-range transport” of industrial chemicals and pesticides came into focus when Persistent Organic Pollutants (POPs) were detected in the remote and assumedly pristine areas of the Arctic. Analytical chemists were interested in measuring concentrations (Ballschmiter and Wittlinger, Ballschmiter, AMAP), and environmental modellers tried to simulate the environmental movement of chemicals in multimedia fate models (Wania and Mackay, Cowen et al., Scheringer, Wania). Persistence and long-range transport potential were identified as the intrinsic chemical properties responsible for environmental migration. Transportation over the atmosphere is most probably the fastest route to worldwide distribution, and photo-degradation is the most likely elimination process of air-borne chemicals. Rivers and ocean currents transport chemicals much more slowly, particularly hydrophilic substances that are less volatile. Wash-out, especially of aerosol-bound chemicals, temporarily removes persistent chemicals from the atmosphere, but not from the environment. They may re-enter the troposphere by re-volatilisation from soil and surface waters (grasshopper-effect). Physical environmental sinks such as river or ocean sediments do not reduce the persistence because they do not eliminate the chemical from the environment.

How did the administrations react to this new environmental threat?

The administrative community had already reacted in November 1979, when the United Nations Economic Commission for Europe convened a High-level Meeting in Geneva in response to acute problems of transboundary air pollution through acidification. It resulted in the signature of the Convention on Long-range Transboundary Air Pollution by 34 Governments and the European Community. The Convention was the first international legally binding instrument to deal with problems of air pollution on a regional basis. The Convention set up an institutional framework bringing together research and policy. Under this Convention, on 24th June 1998 in Aarhus, Denmark, the UN ECE adopted the Protocol on Persistent Organic Pollutants (POPs). It focuses on a list of 16 substances that have been singled out according to agreed risk criteria. The substances comprise 11 pesticides, two industrial chemicals and three by-products/ contaminants. The ultimate objective is to eliminate any discharges, emissions and losses of POPs. The Protocol bans the production and use of some products outright (aldrin, chlordane, chlordecone, dieldrin, endrin, hexabromobiphenyl, mirex and toxaphene). Others are scheduled for elimination at a later stage (DDT, heptachlor, hexachlorobenzene, PCBs). Finally, the Protocol severely restricts the use of DDT, HCH (including lindane) and PCBs. The Protocol includes provisions for dealing with the wastes of products that are banned. It also obliges Parties to reduce their emissions of dioxins, furans, PAHs and HCB below their 1990 levels (or an alternative year between 1985 and 1995). For the incineration of municipal, hazardous and medical waste, it lays down specific limit values. Since it was enforced in October 2003 several “new” POP candidates have been added to the Protocol (http://www.unece.org/env/popsxg, May 2006).

In May 1995 the UNEP Governing Council was “aware that persistent organic pollutants pose major and increasing threats to human health and the environment” and adopted Decision 18/32 on Persistent Organic Pollutants and

“Invited, … the Intergovernmental Forum on Chemical Safety to develop recommendations and information on international action, including such information as would be needed for a possible decision regarding an appropriate international legal mechanism on persistent organic pollutants, to be considered by the Governing Council and the World Health Assembly no later than in 1997.”

(Continues…)

Excerpted from Atmospheric Degradation of Organic Substancesby Walter Klöpffer Burkhard O. Wagner Klaus Günter Steinhäuser Copyright © 2007 by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. Excerpted by permission of John Wiley & Sons. All rights reserved. No part of this excerpt may be reproduced or reprinted without permission in writing from the publisher.
Excerpts are provided by Dial-A-Book Inc. solely for the personal use of visitors to this web site.