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Environ. Sci. Technol. 2005, 39, 683-691

Choosing Chemicals for Precautionary Regulation: A Filter Series Approach ULRICH MU ¨ LLER-HEROLD,* MARCO MOROSINI, AND OLIVIER SCHUCHT Swiss Federal Institute of Technology Zurich (ETH), 8092 Zurich, Switzerland

The present case study develops and applies a systematic approach to the precautionary pre-screening of xenobiotic organic chemicals with respect to large-scale environmental threats. It starts from scenarios for uncontrollable harm and identifies conditions for their occurrence that then are related to a set of amplifying factors, such as characteristic isotropic spatial range F. The amplifying factors related to a particular scenario are combined in a pre-screening filter. It is the amplifying factors that can transform a potential local damage into a large-scale threat. Controlling the amplifying factors means controlling the scope and range of the potential for damage. The threshold levels for the amplifying factors of each filter are fixed through recourse to historical and present-day reference chemicals so as to filter out as many as possible of the currently regulated environmental chemicals and to allow the economically important compounds that pose no large-scale environmental concern. The totality of filters, with each filter corresponding to a particular threat scenario, provides the filter series to be used in precautionary regulation. As a demonstration, the filter series is then applied to a group of nonreferential chemicals. The case study suggests that the filter series approach may serve as a starting point for precautionary assessment as a scientific method of its own.

Introduction On February 2, 2000, the European Commission informed the interested parties of the manner in which the Commission applied or intended to apply the precautionary principle (1). In its attempts to compose a European policy on the application of the precautionary principle, the Commission has funded PrecauPri, a thematic network project conducted under the auspices of the EC’s STRATA Programme. The particular aim of the project was to develop a scientifically sound, politically feasible, legally unambiguous, and democratically legitimated concept of precaution. The concept should provide a policy framework for the implementation of the precautionary principle in different risk areas and ensure specificity and predictability for the various actors involved. Within PrecauPri, the regulation of chemicals was selected as a test case for the design of appropriate procedures in the application of precautionary reasoning. Although there is no single authoritative definition of the precautionary principle, in many of its various formulations * Corresponding author phone: +41-44-6324403; fax: +41-446331136; e-mail: [email protected]. 10.1021/es049241n CCC: $30.25 Published on Web 12/24/2004

 2005 American Chemical Society

four dimensions can be identified (2): (i) a dimension of threat; (ii) a dimension of ignorance, concerning the limits of scientific knowledge; (iii) a dimension of action, concerning the response to the threat; and (iv) a dimension of command, concerning the way in which the action is prescribed. By “threat”, in this context, is meant one or another undesired state of the world. “Ignorance” has a wide range of different meanings, from milder forms of uncertainty about probabilities or incomplete proof of supposed cause-and-effect relations to the most extreme form of “ignorance of ignorance” where the kind of possible unwanted effects itself is unknown (3). This last possibility typically applies to environmental chemicals, where the complete spectrum of possible negative effects is but insufficiently known. However, even if negative effectsssuch as plant toxicity, thinning of eggshells of sea eagles, endocrine disruption, weakening of the immune systemsare largely unknown, there may be sufficient knowledge of so-called amplifying factors that can serve as a basis for precautionary action. It is the amplifying factors that transform, for example, toxicity into a large-scale environmental threat. Toxicity, by its very nature, is first of all a local phenomenonsone organism is exposed to a possibly toxic dose of a substance at a given instance and a given place. However, amplifying factors such as mobility, bioaccumulation, and persistence of a substance can transform its toxicity into a nonlocal, possibly global large-scale problem. The amplifying factors then generate the large-scale nature of the respective management problems. If, eventually, perhaps even a long time after release, an apparently innocuous persistent and mobile chemical has negative biological effects, it is impossible to eliminate it from the environment. The resulting situation would be uncontrollable because even immediate phasing out may not ameliorate the situation quickly enough for some species. The PCBs and the extinction of the European otter (Lutra lutra) can be regarded as an example of this behavior (4). This leads to the central idea of precautionary regulation. It considers large-scale threats arising from uncontrollable situations in case of eventually discovered adverse effects. It is a regulation based on reliable scientific knowledge of amplifying factors but prior to knowledge of adverse effects. It is tailored to situations where no immediate action would solve the problem if any novel adverse effect is discovered. Although persistence is an amplifying factor of this kind, one has to recognize that the long-term presence of a chemical or product alone does not lead to possibly uncontrollable environmental situations of said type. (This can be seen from the examples of concrete, bitumen, plastics, etc.) Only in combination with other amplifying factors, such as mobility, does persistence play a significant role as indicator for large-scale chemical threats. These observations are used to propose a general approach to precautionary regulation by controlling amplifying factors of adverse effects instead of controlling adverse end points directly (5).

Precaution and Chemical Risk Assessment The current practice of chemical risk assessment centers around the identification of risks for human health and the environment (6). The detailed outcome of the assessment procedure then leads to specific regulations depending on exposure, tonnage, and use pattern. The present case study aims at complementing this procedure by a precautionary pre-screening stage (Figure 1). Regulations on the basis of precautionary assessment are necessarily controversial, mainly due to the dimension of ignorance and uncertainty. Since stakeholders in public VOL. 39, NO. 3, 2005 / ENVIRONMENTAL SCIENCE & TECHNOLOGY

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FIGURE 1. Extended chemical assessment including pre-screening. A chemical not screened out by one of the filters proceeds to standard chemical assessment.

FIGURE 2. Scheme of a series of four filters for pre-screening with respect to large-scale environmental impact. debates or in courts of law are not experts in this field, arguments and methods have to be transparent, simple, and intuitivesin addition to being scientifically correct. This excludes black-box-type computer calculations, highbrow mathematics, and esoteric chemical details. Furthermore, measures should concentrate on serious threats where “waitand-see” strategies cannot be justified. The history of the Montreal Protocol on ozone-depleting substances shows that restrictions on the basis of precautionary arguments can be accepted even by stakeholders with opposite interests if the threats are important and action is urgent. Along these lines, we present a filter series procedure for precautionary pre-screeening of organic chemicals with respect to large-scale environmental threats. Each filter is designed to screen for one particular threat scenario (which helps intuition). Accordingly, there is a one-to-one correspondence between threat scenarios and filters. The amplifying factors entering the filters are calculated by inserting measurable physicochemical constants into simple and theoretically sound formulas (transparence), and the calibration of the filters makes optimal use of historical experience with environmental chemicals (relevance). The overall outcome is independent of the filter ordering, and new threat scenarios can be taken into account without questioning earlier results that led to the elimination of suspect compounds (upward compatibility). Substances not filtered out by any of the filters continue on to standard chemical assessment.

Large-Scale Threat Scenarios and Filters Originally, the PrecauPri case study provided a fourmembered filter series for pre-screening: Pandora, Cold Condensation, Transformation Pandora, and Bioaccumulation (Figure 2). The Pandora scenario relates to enduring ubiquity of environmental chemicals. The Cold Condensation or Cold Trap scenario considers the selective accumulation of environmental chemicals in low temperature areas, first of all in the polar regions. In addition to a domain of direct impact, environmental chemicals have a second, naturally more extended domain of influence due to their transformation products in the environment. The Transformation Pandora scenario, accordingly, deals with the enduring 684

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ubiquity of these secondary compounds, using the results of Quartier and Mu ¨ ller-Herold (7) and of Fenner et al. (8). The threat scenario related to Bioaccumulation is given through the possibility of substances to have adverse effects on living organisms even if their concentration in the oceans, lakes, rivers, or in the atmosphere is extremely low. If a bioaccumulating and persistent chemical has negative biological effects, it is impossible to eliminate it from the biosphere, and the resulting situation is as uncontrollable as in the Pandora scenario. Due to the data situation, the present case study restricts itself to a combination of only Pandora and Bioaccumulation. (An introduction to Transformation Pandora and Cold Trap is provided in Section 5 of the Supporting Information, and an example of a three-filter sequence including Transformation Pandora is provided in Section 6 of the Supporting Information.) Pandora. The Pandora scenario is named after the Greek myth of Pandora’s box, which held all evils and complaints. When the box was opened, its contents were unleashed upon the world, causing irreversible harm. The enduring ubiquity of persistent organic pollutants (POPs) is regarded as the epitome of the Pandora scenario (9). For the construction of a related filter, one observes that the Pandora scenario is essentially due to the interplay of mobility and longevity. The potential for mobility and longevity is expressed by two proxy measures: characteristic isotropic spatial (CIS) range (F) and characteristic isotropic global (CIG) half-life (τ). Characteristic isotropic spatial (CIS) range F is the typical distance a molecule would travel before degradationsunder earth-like but spatially isotropic conditions where concentrations quickly equilibrate between the atmosphere, the surface layer of the oceans, and the upper layer of the soil (see Appendix). Characteristic isotropic global (CIG) half-life τ is the typical overall lifetime of a molecule under conditions as for F (see Appendix). (The joint use of spatial range and persistence in chemical assessment goes back to Scheringer and Berg (10). (For details of the subject and its history, see Scheringer (11) and references therein.) Bioaccumulation. Bioaccumulation (12) is a phenomenon combining bioconcentration and biomagnification. Bioconcentration relates to the partition of a chemical between an organism and a surrounding inorganic medium (e.g., leaves/ air, fish/water). Biomagnification denotes the heterotrophic enhancement of concentration in subsequent elements of the food chain (grass/cow, cow/man). As fat tissue is the relevant storage medium in living organisms and as octanol is the chemical proxy usually representing organismic fat, bioconcentration is related either to a chemical’s octanol-water partition coefficient (Kow) or to its octanol-air partition coefficient (Koa ) Kow/K′), with K′ ) KH/RT being the chemical’s dimensionless Henry’s law constant. Kow is a direct measure for bioaccumulation from water into aquatic species, whereas Koa is a direct measure for bioaccumulation into plants from air. In order not to classify the Montreal gases as bioaccumulatingswhich they definitely are notsKoa is preferred to Kow. (For details of this choice, see Section 8.1 of the Supporting Information.) Analogous to the Pandora scenario, the Bioaccumulation filter is based on two amplifying factors: a combination of high Koa values and increased global characteristic persistence (τ). (To bioaccumulate, a chemical has to survive a minimal period of time before degradation.)

Filters and Filter Series In the case study, the individual filters were realized as twoparameter classification schemes with three outcomes: “green” (“unconditional clearance”), “yellow” (“conditional clearance”), and “red” (“no clearance”). For filters based on

FIGURE 3. Two-parameter filter with three grades. two parameters x and yswith each parameter x or y having the grades high/medium/lowsthe outcomes are defined using these grades of the two parameters (Figure 3): green (medium/low, low/low, low/medium); yellow (high/low, medium/medium, low/high); red (high/medium, high/high, medium/high). The calibration of filters now consists of defining the parameter grades leading to the filter outcomes green, yellow, and red. For two-parameter filters with three grades for each parameter, one has to find limiting values separating low/ medium and medium/high for the respective filter parameters. If x and y denote the two parameters and xlm, ylm, xmh, and ymh denote the corresponding limiting valuesswhere xlm signifies a limiting value separating low values of x from medium ones and xmh is the corresponding mark at the border between medium and high, etc.sthen the two points, (xlm, ylm) and (xmh, ymh), define a partition of the x-y plane into the required nine rectangular filter domains (see Figure 3), which then are grouped into the three filter scores: green (low/low, low/medium, medium/low), yellow (low/high, high/low, medium/medium), and red (medium/high, high/ medium, high/high). In the case of a series of several filters, the above procedure applies to each filter separately. The outcome of the series as a whole then consists of a list of results for the individual filters that subsequently have to be combined to an overall result. This is performed along the following rules: 1. A substance classified as red by at least one filter definitively constitutes a serious threat, which triggers prevention. Such a chemical should be eliminated (with the possible exception of “life-saving” pharmaceuticals or some intermediates in industrial synthesis if contained under strict safety standards). 2. Green results in all filters open the way to standard chemical risk assessment. Such a result implies that the substance is inconspicuous with respect to the threat scenarios under consideration. 3. The intermediate cases (i.e., yellow results with or without green scores) trigger a variety of procedures, depending on the intended modes of use. Rule 1 is the epitome of the precautionary approach, whereas rule 2 opens the door to current practice. Rule 3 may result in requirements relating to chemical modification (pesticides), restriction of production volume (consumer products), or containment charges (intermediates in chemical synthesis), etc.

Case Study with Two Filters: Pandora and Bioaccumulation The essential difference between one single filter and a series of filters is most easily illustrated by a combination of only two filters: A precarious chemical should get a red score by at least one of the filters. For precautionary regulation, there is no need to receive a red score from more than one filter since one red is regarded as a sufficient condition for preventive measures. Since this distinction becomes trivial in the case of one single filter, one needs at least two filters for its nontrivial demonstration. Additionally, for obvious reasons it has to be required that chemicals known as inconspicuous should be stopped by none of the filters. As an example, the amplifying factors for both the Pandora filter and the Bioaccumulation filter were calculated. For the calculation of characteristic isotropic spatial (CIS) range, characteristic isotropic global (CIG) half-life, and octanolair partition coefficient (Koa) of a chemical, four substancerelated input data are needed (see Appendix): KH, Henry’s law constant (air-water partition coefficient); Kow, octanolwater partition coefficient (descriptor of lipophilicity); ka, degradation rate constant in air; and kw, degradation rate constant in water. On the basis of the data of the top 35 U.S. High Production Volume (organic) Compounds (HPVCs) (13) as paradigmatic examples for chemicals not posing large-scale threats in the environment and a relevant selection of 43 Montreal/Kyoto/ Stockholm compounds as paradigmatic examples for precarious chemicals, the output parameters τ, F, and Koa were calculated. The results are shown in Figures 4 and 5. It turns out that in both scenarios the regulated compounds are well separated from the HPVCs.

Filter Calibration and Filtering Results Following the Filters and Filter Series section, one now has to find the limiting values defining the filter grades for Pandora and Bioaccumulation (which at the same time corresponds to the specification of a level of protection). Generally, limiting values are directly discussed in purely scientific terms. Along these lines, one could try to fix the filter calibration directly. However, the history of medical and environmental threshold values shows that the way to firm, lasting agreements is long and troublesome. To come to a first meaningful estimate, we look at limiting values optimally separating the two sets of reference substancess the 35 U.S. HPVCs and the 43 chemicals of the Montreal/ VOL. 39, NO. 3, 2005 / ENVIRONMENTAL SCIENCE & TECHNOLOGY

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FIGURE 4. Outcome of the Pandora amplifying factors τ (characteristic isotropic global half-life) and G (characteristic isotropic spatial range) for the HPVCs and a relevant selection of the Montreal/Kyoto/Stockholm chemicals. The regulated compounds are well separated from the HPVCs. The dotted line gives the theoretical maximum spatial range at given half-life, obtained by combining CIG half-life with maximal mobility (i.e., eddy diffusion in air). Realistic (i.e., lower) mobility in water and soil leads to points exclusively at the left of the dotted line.

FIGURE 5. Outcome of the Bioaccumulation amplifying factors Koa (octanol-air partition coefficient) and CIG half-life τ for the HPVCs and a relevant selection of the Montreal/Kyoto/Stockholm chemicals. The Montreal/Kyoto/Stockholm chemicals are well separated from the HPVCs. (References and details of the data selection are given in Sections 2 and 4 of the Supporting Information.) Kyoto/Stockholm group. Though rather indirectly, economical and political facts thus enter calibration and complement (pure) science. Algorithms solving the separation problem are the first Jarimo Procedure (Section 3 of the Supporting Information), its refinements (14), and the geometrical method by Schucht (15). The first Jarimo algorithm gives the following separating values: Pandora: F: low/medium, 340 km; medium/high, 8600 km. τ: low/medium, 9 d; medium/ high: 50 d. Bioaccumulation: log Koa: low/medium, 3.27; medium/high, 6.89. τ: low/medium, 6.31 d; medium/high, 641 d. As the filters are calibrated independently, it is hardly surprising that the threshold value for high persistence is different for Pandora (50 d) and Bioaccumulation (641 d). With respect to the large-scale threats in question, there are four basic outcomes. A substance can be 686

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classified as (a) inconspicuous (two green scores) when being inconspicuous (HPVCs); (b) inconspicuous (two green scores) though being precarious (Montreal/Kyoto, etc.); (c) precarious (at least one red score) though being inconspicuous (HPVCs); or (d) precarious (at least one red score) when being precarious (Montreal/Kyoto, etc.). With the above calibration, the pre-screening filtering completely reproduces the present situation (see Table 1; the details are contained in Tables 1 and 2 of the Supporting Information): no HPVC received a red score (which would stop it), and most of them (80%) even were given two green scores (unconditional clearance). Only seven substances (20%) received a yellow score (conditional clearance), indicating that closer examination should follow. Concurrently, each of the universally itemized Montreal/Kyoto/

FIGURE 6. Outcome of the Pandora parameters τ (characteristic isotropic global half-life) and G (characteristic isotropic spatial range) for 11 chemicals of special interest (see Table 3). The dotted straight lines denote the limiting values of 9 and 50 days, respectively, for CIG half-life and 340 and 8600 km, respectively, for CIS range.

TABLE 1. Result of the Chemical Classification Problema reference chemicals classification

HPVCs

Montreal, Kyoto, Stockholm

inconspicuous (green) precarious (red)

80% 0%

0% 100%

a As green + yellow + red add up to 100%, green + red can add to less than 100%, i.e., to 80%.

TABLE 2. Statistics of 2-Fold Cross-Validationa filter

HPVCs in green

HPVCs in red

regulated compds in green

regulated compds in red

Pandora 12.4 ( 1.82 1.0 ( 1.41 0.6 ( 0.55 19.4 ( 1.14 Bioaccumulation 13.4 ( 2.51 1.6 ( 1.14 0.0 ( 0.00 21.2 ( 0.84 a Average ( SD of five different runs in absolute numbers. The average number of HPVCs was 17.5, while the average number of regulated (Montreal/Kyoto/Stockholm) compounds was 21.5.

Stockholm chemicals was given one or two red scores (no clearance), completely in line with the outcome of the above conferences. The calibration for the two filters was validated separately by the repeated 2-fold cross-validation method (16). For this purpose the set of reference chemicals was randomly divided into two approximately equal-size halves, referred to as the training set and the test set. The filter at hand was then calibrated using the chemicals in the training set as the reference chemicals. The desired statistics were calculated by filtering the chemicals of the test set using the filter calibration obtained with the training set. For both filters, the 2-fold cross-validation was repeated N ) 5 times, each time with a different randomly generated training set and test set. Within each run, the following statistics for the test set were calculated: (a) number of HPVCs in green; (b) number of HPVCs in red; (c) number of regulated compounds (Montreal, etc.) in green; and (d) number of regulated compounds (Montreal, etc.) in red. Table 2 shows the results of the five test runs. The repeated 2-fold cross-validation method was chosen due to the small size of the set of reference data. By dividing

the set of reference chemicals in two equal size halves, we obtain the largest simultaneous training set and test set. Repeating the cross-validation several times compensates for the small size of the data set. (As for the question whether equivalent results can be achieved using a so-called Boolean OR operation, see Section 8.2 of the Supporting Information.)

Special Chemicals of Environmental Interest Aside from the two sets of referential chemicals, a selection of chemicals was put together showing some a priori evidence of persistence, bioaccumulation or long-range transport. Some of these special chemicals might be regulated on national levels. As an application of the filter series technique, they were submitted to precautionary pre-screening. The results are shown in Table 3 and Figures 6 and 7. The input parameters of these chemicals and the calculated values of the amplifying factors are shown in Table 4. The three stereoisomers R-HCH, β-HCH, and γ-HCH (lindane) of the insecticide hexachlorocyclohexane are the major components of the once widely used so-called “technical HCH” (benzene hydrochloride, BHC). They are also the most frequently detected HCH isomers in environmental samples and in human fat and milk. Technical HCH is now banned in most industrialized countries, where in contrast lindane, the only insecticidal isomer, is used as an almost pure substance. In the United States, the production of lindane ceased in 1976. R-HCH and γ-HCH are almost ubiquitous in environmental samples from every continent, including polar and pristine regions (17). The three chemicals received a red score both in the Pandora and the Bioaccumulation filters. Although they are widely considered as POPs in scientific literature, the HCHs are not included in the Stockholm Convention. Endosulfan is a polychlorinated cyclodiene insecticide whose use is permitted in most countries because of its relatively rapid degradation in air and water and because of its lower tendency to bioaccumulate if compared to DDT or the HCHs. It passes both filters, receiving a green score from both the Pandora and the Bioaccumulation filters. For an extended appraisal of endosulfan, its transformation productssendosulfan diol, endosulfan sulfate, and endosulfan endolactonesshould also be considered (i.e., endosulfan itself should be sent through the Transformation Pandora filter). At present, however, physicochemical input paramVOL. 39, NO. 3, 2005 / ENVIRONMENTAL SCIENCE & TECHNOLOGY

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FIGURE 7. Outcome of the Bioaccumulation parameters Koa (octanol-air partition coefficient) and CIG half-life τ for 11 chemicals of special interest (see Table 3). The dotted straight lines denote the limiting values of 3.27 and 6.89, respectively, for log Koa and 6.31 and 641 days, respectively, for CIG half-life.

TABLE 3. Filter Series Performance of 11 Chemicals of Special Environmental Interesta chemicals of special environmental interest

CIS range (km)

Pandora CIG half-life (d)

R-HCH β-HCH γ-HCH endosulfan carbaryl carbofuran HMDS OMCTS (D4) DMCPS (D5) HBB DBDE

medium: 340-8600 km medium medium medium medium low low medium medium medium medium medium

medium: 9-50 d high high high low low low low low low high high

a

Pandora filter

red red red green green green green green green red red

log Koa

Bioaccumulation CIG half-life (d)

Bioaccumulation filter

medium: 3.27-6.89 high high high medium high high medium medium medium high high

medium: 6.3-641 d medium medium medium low low low low low low medium high

red red red green yellow yellow green green green red red

The lower and upper limiting values of the amplifying factors are listed in the second row.

TABLE 4. Physicochemical Input Parameters and Calculated Values of the Amplifying Factors for 11 Chemicals of Environmental Interest chemicals of special environmental interest R-HCH β-HCH γ-HCH endosulfan carbaryl carbofuran HMDS OMCTS (D4) DMCPS (D5) HBB DBDE

KHenry (Pa‚m3/mol)

log Kow

log Koa

kair (1/s)

kwater (1/s)

CIS range (km)

CIG persistence (d)

1.24E+00 7.53E-02 5.21E-01 6.59E+00 3.31E-04 3.13E-04 4.59E+03 1.19E+04 3.10E+04 2.21E+00 1.21E-03

3.80 3.78 3.72 3.83 2.36 2.32 4.20 5.10 5.20 6.07 5.24

7.10 8.30 7.40 6.41 9.23 9.22 3.93 4.42 4.10 9.12 11.55

1.36E-07 1.32E-06 1.84E-07 8.00E-5 5.15E-05 2.80E-05 1.34E-06 9.80E-07 1.50E-06 1.12E-08 1.69E-07

1.08E-07 6.32E-08 6.32E-08 1.73E-06 1.89E-06 2.14E-06 0.00E+00 0.00E+00 0.00E+00 5.35E-07 2.94E-08

6209 2169 5332 428 200 188 3321 3883 3139 4577 1648

79.6 101.7 113.6 0.2 4.3 3.8 6.0 8.2 5.4 636.3 1937.2

eters for the respective transformation products are not available. Carbaryl and carbofuran are the most widely used carbamate insecticides. Because of their rapid degradation in air and water (due to photooxidation, photolysis, hydrolysis, and biodegradation) and their low tendency to 688

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bioaccumulate, their potential for persistence and long-range transport is supposed to be low. Both chemicals pass the filters, receiving a green score in the Pandora filter and a yellow one in the Bioaccumulation filter. For an extended appraisal of carbaryl and carbofuran, their transformation products carbofuran phenol, 3-hydroxycarbofuran, and

3-ketocarbofuran should be considered. Again, the necessary input parameters for these compounds are not available. On the basis of environmental monitoring and general ecotoxicological considerations, a possible role of silicon compounds as a general new class of “environmental chemicals” has been postulated (18). It is then interesting to test the precautionary filter procedure on some of these compounds, such as hexamethyldisiloxane (HMDS), octamethylcyclotetrasiloxane (OMCTS or D4), and decamethylcyclopentasiloxane (DMCPS or D5), which are man-made special representatives of the silicones, commonly referred to as polymethylsiloxanes. HMDS is a constituent of cosmetic and personal care products, hydraulic fluids, and serves as a starting material in the production of other silicone compounds such as D4. D4 is found in soft drinks, cosmetics, detergents, and polishes, whereas D5 is an ingredient of hair care products, antiperspirants, cosmetics, and toiletries. Their environmental behavior and fate is characterized by moderate volatility, low reactivity in soil and water, and an estimated high potential for bioaccumulation. Environmental degradation seems to occur only in the air (through photooxidation by hydroxyl radicals). In water and soil, they are considered nonreactive with respect to hydrolysis and biodegradation. They all pass the filters with a green score. Brominated compounds such as polybrominated diphenyl ethers (PBDE) are widely used as flame retardants in consumer products. They have been detected in environmental and human milk samples in industrialized countries, with increasing concentrations in the past decades. Two of them are submitted to the two-filter procedure. Hexabromobenzene (HBB) is used as flame retardant in polymers. It is not expected to be degraded by direct photolysis, hydrolysis, chemical oxidation, or biological activity. Some degradation in seawater inocula was reported. Its slow degradation in air through photooxidation by hydroxy radicals could be retarded, hexabromobenzene being expected to exist solely on the particles of the troposphere (insofar preventing the reaction with hydroxy radicals). Data on bioaccumulation are controversial, showing potential bioaccumulation only in long-time studies. It was suggested that nonaccumulation was due to the size of hexabromobenzene, resulting in lack of membrane permeation. Hexabromobenzene is retained by both the Pandora and the Bioaccumulation filters (two red scores). Decabromodiphenyl ether (DBDE) is used as flame retardant in textiles, rubbers, and virtually every class of polymers (ABS, PVC, polyamides, polyesters, polyolefins, etc.) It degrades in air, water, and soil only in the presence of sunlight. Hydrolysis and biodegradation have not been reported. Statements concerning the potential for bioaccumulation are inconsistent (19). It is retained in both the Pandora filter (red score) and the Bioaccumulation filter (red score). Debromination of decabromodiphenyl ether leads to the lower brominated congeners, tetra- to hexabrominated diphenyls, which readily bioaccumulate. It is unclear what proportion of the lower brominated congeners in the environment are breakdown products of DBDE and what proportion comes from the commercial penta-BDE mixture.

What Has Been Achieved? First, a kind of scenario technique was used as a basis for precautionary regulation: Scenarios for uncontrollable harm were identified as situations to be avoided. The quantitative representation of scenarios is achieved through filters. Each filter is defined via a small set of relevant assessment parameters. Then, a filter series approach was presented, which is an alternative to the familiar risk-benefit valuations in situations where risks (i.e., probability times magnitude of adverse

effects) cannot be specified because the spectrum of the adverse effects is largely unknown. As a formal scheme the filter series procedure is independent of particular hazards. Next, in a case study dealing with special features of largescale hazards of organic chemicals, two types of twoparameter filters have been constructed and suitably calibrated. The sequence of two filters was shown to reproduce in a shortcut essential results of a long and cumbersome historical development. (A short preview on precautionary filters and Pandora filtering was provided by Mu ¨ ller-Herold; 20.) In the given context of large-scale threats, the respective assessment parameters play the role of amplifying factors. The interplay of amplifying factors in the diverse threat scenarios is then taken into account using two-parameter filters. Two-parameter filters compensate for the onesidedness of limiting values for single assessment parameters: In the Pandora scenario, the interplay of the two parameters prevents concrete, bitumen, and plastics from being eliminated on the basis of persistence (as their mobility is too low), and in the Bioaccumulation scenario they keep the silicones from being eliminated on the basis of high Kow values (as their lifetime is too short). The usual practice of defining limiting values for individual parameters through a body of experts was then complemented by a kind of self-calibration of filters on the basis of reference chemicals with broadly accepted, unequivocal international regulatory status. These sets of chemicals are comparably small and cannot be easily extended without loss of regulatory status. Calibration and validation have to properly deal with this situation. However, if industry finds that thresholds thus obtained are too low or NGOs think they are too high, calibration can be altered by political decision makers (without questioning the precautionary prescreening procedure as a whole.) Such new calibrations, though, would not be based on the Montreal/Kyoto/ Stockholm Protocols or the U.S. HPVCs, and a new consensus would have to be found at an international level (due to the WTO). In cases of several scientifically equivalent methods, we consistently chose the one that was likely to be more suitable for public debate, as citizen participation is one of the declared objectives of the EU. Accordingly, closed analytical formulas were preferred to numerical computer calculations whenever possible. For this purpose we developed concepts such as CIG range, CIS lifetime, CCP cold condensation potentials, secondary ranges, etc. The references cited and the Supporting Information allow the interested reader to get an idea of these concepts. The mathematics for their derivation can be found in more technical papers in Environmental Science and Technology and Ecological Modelling, respectively. Finally, a first look on a group of nonreferential chemicals of special environmental interest links up to the discussion of nonreferential compounds. To conclude, a procedure is presented that fits into the general architecture of the PrecauPri model, building on the three pillars of screening, appraisal, and management (21). The model was developed in a cooperation of social scientists specialized in risk and uncertainty issues, natural scientists, and a legal scholar with special expertise in risk regulation. It honors and carries forward the EU’s philosophy of precautionary policies and good governance and may be used as a template for precautionary risk regulation within and beyond the EU context.

Outlook Although the approach to precautionary pre-screening presented here was developed as an answer to the needs of regulative authorities, a far more extended application is conceivable: Ideally, a chemist designing a new compound on paper could directly “send it through the filters”. At this VOL. 39, NO. 3, 2005 / ENVIRONMENTAL SCIENCE & TECHNOLOGY

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early stage, of course, the measurable input parameters have to be replaced by theoretical or estimated values. In combination with a suitable software solution, a first preliminary precautionary pre-screening could be undertaken directly after the molecule has first appeared on a chemist’s drawing table. In this way, precaution could come into playsprior to the synthesis of one single molecule of a precarious substance. This would be prevention at the source.

Note Added in Proof The authors want to draw the readers’ attention to a recently published paper by P. Sandin et al. (27), which opens a different perspective to precautionary regulation of chemicals.

Acknowledgments This work was funded under Grant BBW-NR. 00.0487 of the Swiss Federal Office for Education and Science. The authors are indebted to Susanna Bucher (Zurich) for technical support, Martin Scheringer (Zurich) for valuable discussions, and Toni Jarimo (Helsinki) for his contributions to calibration and validation.

Appendix Spatial Range and Persistence. A closed analytical formula for characteristic isotropic spatial (CIS) range F has been derived by Mu ¨ ller-Herold and Nickel (22):

{

F ) exD/k tanh(πrxk/D) exp

xk/D

π/2 - 2 arctan[eπr

sinh (πrxk/D)

}

]

with

D/k )

DaVa + DwKwaVw + DsKsaVs kaVa + kwKwaVw + ksKsaVs

For characteristic isotropic global (CIG) half-lives (τ), the formula

τ)

ln 2 , k∞

def

k∞ )

kaVa + kwKwaVw + ksKsaVs Va + KwaVw + KsaVs

was used. The symbols denote the relevant unit world parameters and the substance-related quantities. Unit World Parameters. r ) 6381 km is the radius of the earth, which entails that πr ) 20 037 km is the maximally possible spatial range. The calibration of the unit world’s relative compartment volumes (Vi) and eddy diffusion constants (Di) are taken as compartment

Di (km2 s-1)

Vi (m3)

water (w) air (a) soil (s)

0.01 2 0

233 200 000 1

Substance-Related Input Quantities. ka, kw, and ks are the degradation rate constants for air, water, and soil, respectively. If Kij ) cieq/cjeq denotes the equilibrium partition between compartments i and j, then Kwa and Ksa are the water-air and soil-air partition coefficients. Kwa and Ksa are obtained from a chemical’s Henry’s law constant KH (in Pa m3 mol-1) and octanol-water partition coefficient Kow by

Kwa ) RT/KH Ksw ) focKoc ) 0.02 × 0.41Kow Ksa ) KswKwa 690

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Following Karickhoff (23), the fraction foc of organic carbon in soil is set to 0.02. The factor 0.41 converts the octanolwater partition coefficient into the organic carbon-water partition coefficient Koc; Ksw is the soil-water partition coefficient. The Henry’s law constants are taken for distilled water. Seawater corrections, usually giving an increase of 20-40%, are neglected. As this applies to all substances, it enters the filter calibration and does not lead to arbitrary distortions. For legal considerations, degradation constants (ks) in soil are set to zero. As soil is a highly inhomogeneous medium, degradation constants in soil are not justiciable (i.e., liable to be tried in a court of justice). Their inclusion would undermine legal certainty. This choice of ks leads to slightly increased CIS ranges and CIG half-lives. In the context of precautionary pre-screening, it always leads to results on the safe side, accordingly. As the assumption applies to all substances, it enters the filter calibration. Testing its influence on the output, results have shown that in most cases it has no visible effect. (The inhomogeneity argument is not applied to the soil-water partition coefficient as the Karickhoff procedure seems to be generally accepted. Soil, accordingly, enters the scenario as a lipophilic storage medium.) Comments: CIS Ranges. The CIS ranges are based on a three compartment isotropic global unit-world scenario involving the main global compartments: the troposphere, the surface water of the oceans, and the upper layer of the soil. The concept of CIS ranges was first introduced by one of the present authors (U.M.H.) together with M. Scheringer and M. Berg 10 years ago (24) and is preferred to simpler methods based on single media lifetimes, which can give wrong results. (For details, see Section 8.3 of the Supporting Information.) Comments: CIG Half-Lives. The τ formula with k∞ has been used for a long time in environmental and other multicompartment models. It is a direct consequence of the socalled instant equilibrium assumption presuming rapid equilibration of the chemical potentials of a substance in the respective compartments. A widely known application of the instant equilibrium assumption is gas chromatography. It has been demonstrated by Mu ¨ ller-Herold (25) and Mu ¨ llerHerold et al. (26) that half-lives based on the instant equilibrium assumption (i) are highly precise in the case of rapid exchange between the compartments; and (ii) in all cases they give an upper value to real half-lives calculated without the instant equilibrium assumption in more extended models with corresponding input parameters. If used in precautionary pre-screening, the formula always gives results on the safe side, accordingly. The CIG half-lives as used in the present setup are based on a three-compartment isotropic global unit-world scenario involving the main global compartments: the troposphere, the surface water of the oceans, and the upper layer of the soil.

Supporting Information Available Physicochemical input parameters, calculated values of the amplifying factors, and filtering results of the reference chemicals; details of the first Jarimo procedure for filter calibration and a digression on uncertainty aspects of the present approach; a sketch on complementing filters (Transformation Pandora, Cold Condensation) and on a three-filter sequence; an outlook on REACH, the three-level testing and regulatory system presently discussed in the EU; an account of several discussions with reviewers of this paper. This material is available free of charge via the Internet at http:// pubs.acs.org.

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Received for review May 21, 2004. Revised manuscript received September 24, 2004. Accepted October 13, 2004. ES049241N

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