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Spatial differentiation in LCA impact assessment

9. Ecotoxicity

• 9.1 Introduction
• 9.2 Classification
• 9.3 EDIP97 characterisation factors
• 9.4 EDIP2003 factors for ecotoxicity
• 9.5 Site-generic characterisation
• 9.6 Site-dependent characterisation
• 9.7 Interpretation
• 9.8 Example

Background information for this chapter can be found in:

• Chapter 6 of the "Environmental assessment of products. Volume 2: Scientific background" by Hauschild and Wenzel (1998).
• Chapter 8 of the "Background for spatial differentiation in life-cycle impact assessment – the EDIP2003 methodology" by Potting and Hauschild (2005).

9.1 Introduction

Chemical emissions contribute to ecotoxicity if they affect the function and structure of the ecosystems through toxic effects on the organisms living in them. Ecotoxicity involves many different mechanisms of toxicity and compared to the other environmental impacts included in life cycle impact assessment, ecotoxicity has the character of a composite category which includes all substances with a direct effect on the health of the ecosystems. On this basis, the list of substances classified as contributing to ecotoxicity will be much more comprehensive than the corresponding lists of the other environmental impacts (apart from human toxicity which is of a similar nature), and it will include many different types of substances with widely differing chemical characteristics. For a substance to be classified as ecotoxic, it must be toxic to some of the natural organisms, but toxicity is a relative concept, and paraphrasing the ancient Swiss physician Paracelsus, all substances are toxic if the dose ingested is large enough. Apart from the substance's toxicity, properties like persistence (low degradability in the environment), and ability to bioaccumulate or be transported to sensitive parts of the environment, therefore determine, which substances are considered to be ecotoxic. Together with the direct toxicity, these properties are of decisive significance for whether the dose is large enough to result in the occurrence of ecotoxic effects.

9.2 Classification

For the classification of substances contributing to ecotoxicity, a screening tool has been developed as part of EDIP97 based on the substance characteristics discussed above. It is recommended to use this tool in combination with some of the existing lists of priority pollutants like the List of Undesirable Substances and the Effect List (Danish EPA, 2000a and b).

9.3 EDIP97 characterisation factors

The EDIP97 method (Wenzel et al., 1997, Hauschild et al., 1998) is a simplified version of what has later been called a modular approach to ecotoxicity assessment. Rather than basing it on adaptation of one of the existing multimedia models developed and used for generic risk assessment of chemicals, the approach behind the EDIP97 method is to identify those properties that are important for the substance's potential for ecotoxicity and then include these in a transparent and relevant way in the expression of the characterisation factor.

Ecotoxicity is considered in aquatic ecosystems (acute and chronic), in terrestrial ecosystems (chronic exposure) and in wastewater treatment plants. For each endpoint, a simplified fate modelling is applied based on a modular approach where redistribution between the environmental compartments and potential for biodegradation are represented as separate factors. The characterisation factor for chronic ecotoxicity in environmental compartment (n) from an emission of substance (i) to compartment (m) is determined as:

(9.1)

.... where the redistribution factor, f^mn expresses which fraction of the emission, upon redistribution from the initial compartment (m), reaches the final compartment (n), where the ecotoxic impact is modelled. BIO represents the potential for biodegradation as determined from standardised tests for ready and inherent biodegradability. The toxicity is expressed as the inverse predicted no effect concentration (PNEC) for the ecosystems of compartment (n).

As described in the introduction to this Guideline, the EDIP97 methodology is prepared for inclusion of spatial differentiation for all the non-global impact categories through site factors SF intended to modify the site-generic characterisation factors. For ecotoxicity assessment, the expression becomes

(9.2)

The site-generic impact potential in EDIP97 is interpreted as the largest impact to be expected from the emission and the site factor is seen as the spatially determined probability that the full impact will occur, i.e. SF ranges between 0 and 1. The EDIP data format is open for inclusion of spatial aspects into the characterisation, and Wenzel and co-authors give guidance on the quantification and use of the SF without making the site factor really operational (Wenzel et al., 1997).

The EDIP methodology for ecotoxicity assessment also involves other possibilities for spatial differentiation. For the fraction of airborne emissions that deposit, the redistribution factor, f^mn is set at "a" when (n) is the aquatic compartment and 1-a when (n) is the terrestrial compartment. EDIP97 allows "a" to be chosen according to the conditions of the region where the emission takes place. For Danish conditions, a=0.5 is proposed while a global default is set at a=0.2.

Furthermore, in EDIP97, spatial information in the form of initial dilution data for waterborne emissions, is suggested included as technical information in the weighting of the potential contribution to acute aquatic ecotoxicity to reflect the differences in dilution potential (and hence the probability of acute effects) for different types of aquatic systems.

9.4 EDIP2003 factors for ecotoxicity

The EDIP2003 factors do not replace the EDIP97 characterisation factors. Rather, they should be considered as exposure factors to be used in combination with the EDIP97 factors which are maintained to characterise the site-generic impact on ecotoxicity from emissions. This means that the parts of the fate and effect factors which are not spatially differentiated are maintained as they were defined in EDIP97. For inclusion of spatial variation, the site factor framework of the EDIP97 has been attempted made operational. Since no integrated assessment model has been found for adoption to spatial differentiation in the modelling of substance fate, the simplified modular approach employed in EDIP97 has been extended into the field of the exposure assessment instead. Based on an analysis of the causality chain for ecotoxicity, the main spatial characteristics influencing the environmental fate or ecotoxic effect of substances have been identified and the possibility for including them in the characterisation of ecotoxicity has been examined.

A framework has been developed for inclusion of the spatial variation in average ambient temperature (biodegradation), frequency of natural ecosystems in soil and water (target systems) and sorption and sedimentation conditions between fresh water and salt water systems (removal). The framework has been made operational for four European regions: North, East, West and South.

Exposure factors for ecotoxicity
The already existing site-generic characterisation factor are interpreted as representing the impact from the substance assuming that exposure takes place. The spatial characterisation is thus performed by multiplying the site-generic characterisation factor and an exposure factor, which is seen as a modifier expressing the degree to which exposure actually occurs. The ecotoxicity exposure factor is abbreviated EEF for the sake of consistency with the exposure factors for other impact categories defined in EDIP2003. It depends both on the substance properties and the spatial characteristics of the process and is expressed as a product of the following variables:

• SF_emis representing the spatial variation of the parameters (descriptors) of the emission part of the cause-impact chain
• SF_bio representing the spatial variation of the biodegradation and other transformation parameters in the fate part of the cause-impact chain
• SF_sed representing the spatial variation of the sorption and sedimentation parameters in the fate part of the cause-impact chain (only relevant for aquatic ecotoxicity).

(9.3)

Exposure factors are calculated for ecotoxicity in water and soil in Annex 9.4.

9.5 Site-generic characterisation

The site-generic exposure factors for ecotoxicity are taken as the average values from Tables 9.1 (for aquatic ecotoxicity) and 9.2 (for terrestrial ecotoxicity). The site-generic ecotoxicity impact potentials are calculated using these factors in combination with the relevant EDIP97 characterisation factors for ecotoxicity from Wenzel et al. (1997), according to the following expression:

(9.4)

Where:

sg-EP(etn) = The site-generic ecotoxicity impact from the product (in m³/f.u.) in environmental compartment n

sg-EEF_s = The site-generic exposure factor (dimensionless) relating the emission of substance (s) to the exposure, sg-EEF_wc = 1.3 for organic substances and 0.91 for metals and sg-EEF_wc = 0.33, determined as the average values for the European regions in Table 9.1 and 9.2.

CF(etm,n)_s = The EDIP97 characterisation factor for ecotoxicity (in m³/g) from Annex 9.1, 9.2 or 9.3 which relates the emission of substance (s) into the initial media (m) to the impact in compartment n

E(m)s = The emission of substance (s) to the initial media (m) (in g/f.u).

9.6 Site-dependent characterisation

The exposure factors are modifying factors representing the severity of the exposure similar to the factors developed for the impact categories human toxicity and aquatic eutrophication. Given the moderate range between the highest and the lowest site-dependent exposure factors for organic substances in Table 9.1, and given that considerable uncertainties accompany the exposure factors developed for ecotoxicity, it is found that the additional uncertainties may well exceed the variation given by these exposure factors.

On this background, there is only little motivation for performing a full site-dependent exposure assessment for ecotoxicity in soil or water. Rather, the site-dependent factors should be seen as an information for a sensitivity analysis and possibly also for reduction of the potential spatial variation in the site-generic impact.

The Guideline will recommend that their application will be for sensitivity analysis to help quantify the possible spatial variation underlying the site-generic impact potentials

For emission of metals to water, the situation is a bit different. Here, the type of receiving environment strongly influences the loss through sedimentation for the most adsorbing metals, in the sense that emissions to rivers and lakes have a much lower exposure factor due to sedimentation in lakes. This deviation from the general pattern of the exposure factors does not alter the overall recommendation that the ecotoxicity exposure factors are used only in a sensitivity analysis context and not in a routine site-dependent characterisation.

The ecotoxicity impact from a given product is in many cases dominated by one or a few processes. Even for applications, where a site-dependent assessment is preferred, it is therefore advised to start with calculation of the site-generic impact of a product as described in the previous section. This site-generic impact can be used to select the processes with the dominating contributions (step 1), and next to evaluate the actual spatial variation in the contribution from these processes by applying the relevant site-dependent factors (step 2 and 3).

Step 1
The site-generic ecotoxicity impact in water or soil, as calculated in the previous section, is broken down into the contributions from the separate processes. These contributions are then ranked from the largest to the smallest contribution, and the process with the largest contribution is selected.

Step 2
The site-generic ecotoxicity impact from step 1 is reduced with the contribution of the process selected in step 1. Next, the site-dependent impact from the emissions of this process is estimated with the relevant site-dependent factors.

(9.5)

Where:

sd-EP(etn)_p = The site-dependent ecotoxicity impact in compartment (n) from process (p)

EEF(etn)_s,i = The site-dependent exposure factor (dimensionless) relating the emission of substance (s) in situation (i) as relevant for process (p) (described by geographical region and location in the hydrological cycle) to exposure at the regional level. The site-dependent exposure factor is found in Annex 9.4 in Table 9.9 of for organic substances and in Table 9.10 for metals.

CF(etm,n)_s = The EDIP97 characterisation factor for ecotoxicity (in m³/g) from Annex 9.1, 9.2 or 9.3 which relates the emission of substance (s) into the initial media (m) to the impact in compartment n

E(m)_s = The emission of substance (s) to the initial media (m) (in g/f.u).

The determining parameters are the region of emission (Northern, Western, Eastern, and Southern Europe) and type of receiving water for emissions to water (river or lake, estuary, sea, influencing SF_sed) and a number of substance characteristics (biodegradability, lipophilicity and volatility).

For emissions of organic substances or metals to air, the part which ends up in water is assumed to deposit mainly in the sea and EEF_wc for sea (in Table 9.9 or Table 9.10) is therefore chosen for air-borne emissions.

Step 3
The site-dependent contributions from the process selected in step 1 are added to the adjusted site-generic contribution from step 2. Step 2 is repeated until the site-dependent contribution from the selected processes is so large that the residual spatial variation in the ecotoxicity score can no longer influence the conclusion of the study (e.g. when the site-dependent share is larger than 95% of the total impact score).

9.7 Interpretation

For the exposure factors tabulated in Annex 9.4, the ranges (min-max value) are shown in Table 9.1 for aquatic and terrestrial ecotoxicity of organic substances and in Table 9.2 for metals.

Table 9.1. Ranges (min-max value) and medians of exposure factors for organic substances.

For organic substances it is found that the largest variation, which can be introduced by using this framework for spatial characterisation of aquatic ecotoxicity, is a factor 28 (1.95:0.07 between the value for a not biodegradable substance emitted directly to the sea in Northern Europe and a strongly lipophilic substance emitted to a river in Western Europe). For substances of less extreme lipophilicity (logK_ow<4), the largest variation is a factor 6.5, found between the same two situations. For terrestrial ecotoxicity, the largest variation is a factor 3.7 (0.65:0.18 between the value for any substance emitted to soil in Northern Europe and any substance emitted to soil in Southern Europe).

The variation between highest and lowest exposure factor is thus quite modest, even for extremely lipophilic substances. Indeed, the developed exposure factor is expected to represent only a minor part of the actual spatially determined variation in the fate and resulting exposure of ecosystems to chemicals within Europe since:

• A large number of parameters which potentially contribute to spatial variation could not be included in the framework as explained in Tørsløv et al. (2005). In general, their inclusion was not feasible due to the low availability of environmental data or the current modest state of ecotoxicity modelling. This is the case for differences in ecosystem sensitivities and differences in background loads throughout Europe. If it had been possible to include more of these parameters, it is anticipated that the modelled spatial variation as expressed through the exposure factor EEF would have been larger.
• As argued in Tørsløv et al. (2005), it must be expected that the size of the variation in nature parameters between regions is reduced when the size of the region is increased (the larger the region, the larger the differences within the region and the lower the variation between regions).

This trend will propagate to the exposure factors calculated from selected nature parameters. In the present methodology, for feasibility reasons, Europe has been split into just four regions, and it is foreseeable that if the framework had been based on individual countries rather than such large geographical regions, the modelled spatial variation would have been larger.

For metals, the picture in Table 9.2 is somewhat different from what was observed for organic substances in Table 9.1 mainly due to the occurrence of extremely low exposure factors for the strongly adsorbing metals, particularly lead and tin when emitted to freshwater systems (river, lake) where their removal through adsorption and sedimentation is efficient. For the rest of the metals, the pattern is similar to the pattern for organic substances.

Overall, it is judged that considerable uncertainties accompany the exposure factors developed for ecotoxicity, and that these uncertainties may well exceed the variation given by the factors. On this background, the authors do not find it recommendable to apply the developed exposure factors in an attempt to perform spatial characterisation of ecotoxicity in LCIA.

Furthermore, the emission data for calculating European normalisation references lack the required spatial differentiation for most substances (Stranddorf et al., 2005), and therefore it has not been possible to calculate EDIP2003 normalisation references for any of the ecotoxicity sub categories.

Currently, work is underway in the OMNIITOX project under the fifth Frame Programme of EU on development of a European consensus method for characterisation of ecotoxicity in LCA. This method involves a comprehensive multimedia fate model with the option of spatial differentiation at the level of countries.

Table 9.2. Ranges (min-max value), averages and medians of exposure factors for metals.

The reader with interest in spatial characterisation of ecotoxicity is referred to the results of this work which will be available towards the end of 2004 (www.OMNIITOX.net.).

9.8 Example

In spite of the recommendation given in Section 9.7, the EDIP2003 exposure factors have been applied in a characterisation of the inventory presented in Section 1.6 to illustrate their use.

Site-generic characterisation
As described in Section 9.5, first the site-generic impacts are calculated. The ecotoxicity impacts shown in Table 9.3 are determined according to Equation 9.4, using the EDIP97 factors from Annex 9.1 and 9.2 (for emissions to air and water respectively) and site-generic exposure factors taken as the averages in Table 9.1 and 9.2.

Among the air- and waterborne emissions, EDIP97 factors exist only for the metals but these are also expected to be the strongest contributors to ecotoxicity in water and soil.

Table 9.3. Site-generic impact potentials for chronic ecotoxicity in water and soil for one supporting block made from plastic or zinc, (expressed as volume of exposed compartment).

Using the site-generic EDIP97 characterisation factors, the zinc supporting block has the largest chronic ecotoxicity impact potential in both water and soil. For both supporting blocks, cadmium and zinc emissions to air are the most important contributors to ecotoxicity in water and soil while the waterborne zinc emission also contributes significantly to ecotoxicity in water for the zinc component. In order to shed some light on the influence of the potential spatial variation, site-dependent characterisation is performed for those processes that contribute the most to the site-generic impacts.

Site-dependent characterisation
Table 9.3 reveals that the predominant contributions to the ecotoxicity impact are caused by Cd and Zn to air and (for the zinc component) Zn to air. For the zinc component, the main sources for Cd and Zn emissions to air and water are identified as the production of zinc from ore which takes place in Bulgaria and, for Zn to air, the casting of the component which takes place in Yugoslavia (data not shown). For the plastic component, the Cd and Zn emissions to air originate mainly from the generation of electricity which takes place at a number of places throughout Europe. For the latter it is thus chosen to retain the site-generic characterisation. The emissions from the selected processes contribute about 80% and 95% of the full site-generic impacts of Table 9.3 for the zinc component and the plastic component respectively (data not shown).

In the calculation of the site-dependent impacts for the key processes for the zinc component, the relevant site-dependent regional exposure factors are found in Table 9.10 of Annex 9.4. All the main processes take place in Southern Europe. The results of the site-dependent characterisation are shown in Table 9.4.

Table 9.4. Site-dependent impact potentials for chronic ecotoxicity in water and soil for key processes from the zinc component product system.

The site-generic impacts from these key processes are subtracted from the original site-generic impacts in Table 9.3 and the site-dependent impacts of Table 9.4 are added. The thus corrected ecotoxicity impacts via air are found in Table 9.5 and the difference to the original site-generic impacts of Table 9.3 is illustrated in Figure 9.1.

Table 9.5. Chronic ecotoxicity impacts in water and soil from the zinc component product system with site-dependent characterisation of key process emissions

Site-dependent characterisation slightly increases the size of the aquatic ecotoxicity impact and reduces the terrestrial ecotoxicity impact, but it does not influence the strong dominance of the zinc component over the plastic component. For the zinc-based component more than 90 % of this impact has now been calculated using site-dependent characterisation factors. Even if the site-dependent characterisation was performed for all the remaining processes in the product system, the result would thus not change significantly. The major part of the spatially conditioned potential for variation of the impact has been cancelled.

Figure 9.1 Site-generic and site-dependent ecotoxicity impacts in water and soil.For the site-dependent impacts, the site-dependent exposure factors have only been applied for the key processes as described above.

Click here to see the Figure

Annex 9.1: EDIP97 characterisation factors for ecotoxicity assessment for emissions to air (Wenzel et al., 1997)

Annex 9.1: EDIP97 characterisation factors for ecotoxicity assessment for emissions to air (Wenzel et al., 1997)

Annex 9.2: EDIP97 characterisation factors for ecotoxicity assessment for emissions to water (Wenzel et al., 1997)

Annex 9.3: EDIP97 characterisation factors for ecotoxicity assessment for emissions to soil (Wenzel et al., 1997)

Annex 9.4: EDIP2003 exposure factors for ecotoxicity in water and soil

The exposure factors are calculated applying Equation 9.3:

The individual factors of the exposure factor are discussed below and on this basis the exposure factors are calculated. Background information for the calculation of the individual factors is found in Tørsløv et al., 2005.

The emission component, SFemis

For emissions to air or emissions to water or soil which are found to evaporate, the SFemis factor reflects the fraction of the deposited part of the emission which will expose water or soil ecosystems.

In connection to EDIP97, SF_emis is defined as

Where a is the fraction assumed to deposit to land in the calculation of the site-generic EDIP97 ecotoxicity factor.

SF_emis is calculated based on fractions deposited to water and soil natural areas for the four European regions, assuming the use of a global default value of 0.2 for a in the EDIP97 characterisation factors in Annex 9.1-9.3.

The biodegradation and transformation component, SFbio

The SFbio factor reflects the variation of biodegradability with the average temperature of the region, where the fate of the substance takes place. It is relevant for both aquatic and terrestrial systems. The annual average temperature over Europe varies around 10° C between the Nordic region and the Southern region with the Western and Eastern regions in-between. Assuming that the current site-generic fate modelling (in EDIP97 or other LCIA methodology) corresponds to an average mid-European situation, the SF_bio factor is determined as:

Table 9.6. SFemis for emissions occurring in different regions of Europe.

Southern countries: SF_bio= 0.7
Nordic countries: SF_bio= 1.3
East and Western European countries: SF_bio = 1

The sorption and sedimentation component, SF_sed

The SFsed factor must reflect the spatial variation in the relative importance of sedimentation as a removal process for substances adsorbing to particulate material in different aquatic systems. The SF_sed factor is only relevant for substances emitted to or ending in the aquatic compartment of the environment.

In EDIP97, there is no consideration of removal due to sedimentation. This is equivalent to operating with a removal factor with the value 1 (just like no potential for biodegradation is represented by a BIO factor value of 1).

The removal by sedimentation depends on:
1)The net-sedimentation rate of suspended material in different aquatic systems.
2)The position of the emission point in the hydrogeological cycle.
3)The biodegradability and thus how long time the substance can be expected to be present in the environment.
4)The sorption behaviour of the substance

These parameters are included in the values for SFsed for organic substances presented in Table 9.7 and for metals in Table 9.8.

Table 9.7. SFsed representing removal by the combined effect of sedimentation and biodegradation for readily biodegradable, inherently biodegradable and not biodegradable organic substances of different lipophilicity for the three emission scenarios: emission to river and from there through lake to estuary and sea, emission through estuary to sea and emission directly to sea.

N.B.: Not biodegradable

Table 9.8. SFsed representing removal by sedimentation for different metals in the three emission scenarios: emission to river and from there through lake to estuary and sea, emission through estuary to sea and emission directly to sea.

Ecotoxicity exposure factors, EEF
Based on the SF-values given above, the aquatic ecotoxicity exposure factors are calculated and tabulated for organic substances and metals in Table 9.9 and Table 9.10, and the terrestrial ecotoxicity exposure factors in Table 9.11.

Spatial differentiation in Life Cycle impact assessment - The EDIP2003 methodology

Table 9.9. Site-dependent exposure factors for aquatic ecotoxicity (EEFwc) of organic substances depending on region of emission, lipophilicity, biodegradability (ready, inherent or not biodegradable) and point of emission in the hydrological chain (to river, estuary or sea).

Table 9.10. Site-dependent exposure factors for aquatic ecotoxicity (EEFwc) of individual metals depending on region of emission, and point of emission in the hydrological chain (to river, estuary or sea).

For emissions of organic substances or metals to air, the part which ends up in water is assumed to deposit mainly in the sea and EEFwc for sea is therefore chosen for air-borne emissions.

Table 9.11. Site-dependent exposure factors for terrestrial ecotoxicity (EEFsc) of organic substances and metals depending on region of emission.

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