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Characterisation Method Information

Characterisation Method Name:

Ecotoxic substances soil emissions impact on PDF

Version:

2000

Date Completed:

2000

Principal Method Name:

ECO-indicator: methematical modelling of EUSES and logistic distribution dose-effect curve on PDF

Method Description:

PDF: Potentially Disappeared Fraction

Description of the damage category

Ecosystems are heterogeneous and very complex to monitor. There are a number of treaties and declarations (UNCED, UNEP, Council of Europe), that list attributes that are important to mankind, such as: biodiversity, aesthetic and cultural values, ecological functions and services, ecological
resources and information functions (in genes).
One way to describe Ecosystem Quality is in terms of energy, matter and information flows. If we want to characterise Ecosystem Quality in terms of these flows, we could say that a high Ecosystem Quality is the condition in which the flows are not noticeably disrupted by anthropogenic activities. In contrast, a low Ecosystem Quality is the condition in which these flows are disrupted by anthropogenic activities. The level of disruption is thus the most important parameter to monitor ecosystem quality.

To complicate things further these flows can exist on many different levels. For instance the information flow can be described on the level of ecosystems, species and genes. The material and energy flow can be described in terms of free biomass production, as is proposed in [LINDEIJER ET AL 1998].

It is clear we cannot model all these attributes on all these levels and dimensions. For our purpose, we concentrate on the information flow, on the species level. This means we assume the diversity of
species is an adequate representative for the quality of ecosystems.

Reversible damages

Practically all species groups can be affected by anthropogenic influence. It is impossible to monitor them all. We had to make a choice for the species groups that can be used as an appropriate representative for the total ecosystem quality. Furthermore it is important to choose between:
1. The complete and irreversible extinction of species.
2. The reversible or irreversible disappearance or stress on a species in a certain region during a certain time.
Although the first type of damage is probably the most fundamental damage to ecosystems, it is extremely difficult to model in the LCA context, since it requires information on the exact location of
the last representatives of a species in relation to the location of an impact. In fact we can assume that complete extinction usually occurs as a result of many different factors. This means no single product life cycle causes the extinction, but all the product life cycles together are responsible for the full extinction.
In the second option we assume the damage caused by a product life cycle results in a temporary stress on ecosystems. This stress can be one of the factors that result in a full extinction of a species, but we do not know. The stress caused by a product life cycle is temporary as long as a functional unit is used with a limited time perspective. Such an LCA results in emissions that are expressed as a mass loading and a temporary occupation of an area. Even if habitats are destructed by land conversions we assume this damage will be restored.

The damage to Ecosystem Quality now can be expressed as: the relative decrease of the number of species (fraction)* area * time

Modelling the effect on species groups

The crucial parameter in the model for Ecosystem Quality is the parameter that represents the effect on a species group. Unfortunately we have not been able to find a uniform parameter for this purpose, such
as the DALY. We use two different expressions:
• For toxicity we use the PAF, the potentially Affected Fraction of species, as proposed in [HAMERS ET AL 1996]. The PAF is used to express the effect on (mostly lower) organisms that live in water and soil, such as fish, crustaceans, algae, worms, nematodes, micro-organisms and several plant
species. The PAF can be interpreted as the fraction of species that is exposed to a concentration equal to or higher than the No Observed Effect Concentration (NOEC). It is a measure for toxic stress, and in fact not a real damage, as defined here.
• For acidification, eutrophication and land-use we use the PDF of species, the Potentially Disappeared Fraction. The PDF is used to express the effects on vascular plant populations in an area. The PDF can be interpreted as the fraction of species that has a high probability of no occurrence in a region due to unfavourable conditions. The PDF is based on the POO, the Probability Of Occurrence, as used in [ALKEMADE ET AL 1996] to model the effects of acidification and eutrophication. The PDF is in fact represented by 1-POO. This means the fraction of species that does not occur can also be described as the fraction of the species that has disappeared. For this
project the PDF concept is also used for land-use.
This means we do not have a uniform damage unit for the damage category ecosystem quality, as we have in the damage category Human Health. There are two problems:
1. We use different species groups as representatives for the total ecosystem: vascular plants for acidification, eutrophication and land-use and a broad range of (mostly lower) aquatic and benthic
organisms for toxic effects.
2. We use different levels to determine the effects, the level at which species are affected and the level at which species disappear.
The reasons for modelling damage for different impacts on different species groups are as follows:
• The different impacts are based on separate models. For each model the relation between a specific impact and an effect on the species level is described in a different way, providing the best scientific basis for that specific dose-response relationship.
• For toxic effects in soil and water, the relation between the diversity of aquatic and benthic species and the NOEC derived from laboratory testing is at present the best scientific basis to translate from emissions to toxic effects on the ecosystem level.
• For land-use, acidification and eutrophication the observed occurrence of vascular plants derived from field monitoring is at present the best scientific basis to determine the relation between impact and damage.
Modelling the effect on higher organisms, such as birds and mammals or reptiles is even more difficult, as the species migrate, have complex food patterns, as they are usually at the end of the food chain.
Perhaps most importantly, these species are all very different in their response to stresses; therefore it is hard to treat them as a group. We assume that the occurrence and health of a selection of aquatic and
benthic species and vascular plants, which are usually essential providers for adequate food supply and other habitat characteristics, are a good indicator for the health and occurrence of the higher species.
The reasons for differentiating between potentially affected and disappeared fractions is partially pragmatic: the different models have different results, and partially fundamental :
• In ecotoxicity the NOEC is widely in use to determine the toxic effect. Alternative measures are the Lethal Concentrations, such as LC50 or LC5. These are concentration levels at which 50 or 5% of the population has died. A problem with the LC values is that lower species can rather easily adapt
to higher toxic stress levels. This means the laboratory test used to determine LC values are difficult to translate to conditions in the field, where long-term exposure is dominant. Not enough information from field observations is available to use real observed damage that can be related to
the disappearance of these species.
• It is difficult to establish a measure at which we can say a vascular plant is affected by a certain condition. It is much easier to determine if a species has disappeared or simply cannot exist under
measurable field conditions.

Fate analysis

The fate analysis for ecotoxic substances included in the Eco-indicator 99 methodology is carried out with EUSES(the European Union System for the Evaluation of Substances). The result of the fate analysis is a link between an emission to air, water, agricultural soil and industrial soil and concentrations in water, and pore water of agricultural, industrial and natural soil.

Effect analysis

The method used to calculate damage to Ecosystem Quality is the elaboration of the concept by [HAMERS ET AL 1996], providing an algorithm to calculate the toxic stress on ecosystems denoted as a Potentially Affected Fraction (PAF) of species. The value of PAF indicates the fraction of naturally occurring organisms exposed to concentrations higher or equal to the laboratory NOEC. The toxic stress in a multiple substances exposure situation is indicated by the indicator for toxic effect
substances (Itox), which is in fact equal to the combined PAF or combi-PAF. Secondary poisoning is not incorporated into the PAF calculations. The main exposure route is assumed to be water for aquatic ecosystems and pore water for terrestrial ecosystems. The exposure route through food is considered
not to be important.
A substance specific dose-effect curve, which is representative for the naturally occurring organisms has to be calculated. It is assumed that the dose-effect curve can be described by the log logistic distribution function of NOECs. The log logistic distribution function is estimated from single species toxicity data. The distribution function is based on chronic NOECs. PAF is calculated from the combination of the estimated distribution function and the calculated field concentration.

The combined toxic stress in a multiple stress situation can be calculated according to two methods from the single species combination toxicology, respectively concentration addition and effect addition.
concentration addition can only be applied to inert hydrophobic substances, the mode of action of such substances is called narcosis. Effect addition is applied to all other substances.

Damage analysis

For LCA purposes , a specific way to add up damages from combined emissions of a product system, which is a combination of concentration and effect addition, has been worked out by [MEENT ET AL 1999]. Since spatial and temporal information is not included in LCA, an average background
concentration for all substances, equal in all areas of Europe, has to be assumed. A marginal increase of the concentration of one single substance, resulting from a product system, has only a very small
influence on the average situation in Europe. It is postulated [MEENT ET AL 1999] that the many different chemicals present cause concentration additive effects. According to [MEENT ET AL 1999] the
marginal damage to ecosystems from a marginal increase of the concentration of a single substance depends on the present level of damage from the mixture of substances already present in the environment. This means that the slope of the single substance PAF curve is not relevant, but the slope of the overall PAF curve, based on mixtures of substances, which are present in the European environment, must be determined to assess the marginal damage from an emission.
Such a PAF curve for mixtures can be constructed by standardising the concentrations of individual substances into units of average toxicity of the total mixture, so called Hazard Units (HU). Therefore the marginal concentration increase of a substance must be divided by the average NOEC (=10 a ) for that substance, creating standardised hazard units which are very similar to the well known PEC/PNEC ratios. The effects of different levels of pollution by unknown (but presumably relative invariable)
environmental mixtures, standardised to Hazard Units follow the hypothetical logistic curve. This curve yields the total toxic stress (i.e. the proportion of species for which the NOEC is exceeded = combi-PAF), as a function of the sum of hazard units in the mixture [HAMERS ET AL 1996], which can be viewed as the toxicologically standardised mixture concentration. HU=1 (PEC/PNEC=1) means that all species are exposed to a background level equal to the average NOEC (which is based on the distribution of NOECS of all species). Since 50% of the species has a NOEC below this average, this implies that these 50% of all species are affected. This explains that at HU=1 the potentially affected fraction is 50%.
Based on [ZWART AND VAN DE MEENT 1998], an appropriate standard deviation of mixture toxicity can be found in a ß -value of 0.4. The working point is determined by the slope of the PAF-curve for mixtures at the present level of toxic stress in Europe. According to RIVM (National Institute of Public Health and the Environment (The Netherlands))[MV 1997], ambient levels of combi-PAF in water and soil in the Netherlands are typically 10%-50%. We assume that the European value of combi-PAF lies within the same interval. This means the slope of the curve in the possible working points varies with almost a factor of three with a combi-PAF between 10 and 50%

Since no additional information is available, the geometric mean (24%) is used as average European Combi-PAF.

Toxic Stress (combiPAF)

From the marginal increase of the concentration the marginal increase in hazard units can be calculated. When the working point is determined the marginal damage from the marginal increase in hazard units can be calculated.
The procedure to calculate damage to Ecosystem Quality resulting from an emission can now be described as follows:
• Determine the temporary, marginal increase of the concentration in a specific environmental compartment from the fate model, for each specific substance (A mass loading, as found in inventory table, can only cause a temporary increase in the
concentration).
• Determine the increase in standardised toxicity units (hazard units) from the concentration increase of the substance for each emitted substance that may cause an impact on Ecosystem Quality using the average NOEC of each substance. Add up the total increase in hazard units.
• Choose a reference value for the slope of the combi-PAF curve for substance mixtures representing the present ambient level of toxic stress (working point).
• Determine the temporary marginal damage (in the environmental compartment considered) from the total increase in hazard units using the slope of the combi-PAF function at the workpoint.
Multiply the calculated increase in combi-PAF with the total area of the environmental
compartment.
For one specific emission, this procedure is repeated for the concentrations in all relevant environmental receiving compartments separately (water, agricultural soil, industrial soil, natural soil).

Finally the damages in PAFm2yr of the different compartments can be added up, resulting in the total damage in Europe.

Literature Reference:

1. [Lindeijer et al 1998] Lindeijer, E., M. van Kampen, P. Fraanje, H. van Dobben, G.J. Nabuurs, E. Schouwenberg, D. Prins and N. Dankers (1998). Biodiversity and Life Support Indicators for Land-use Impacts in LCA. Wageningen, Texel, IVAM ER, IBN-DLO. Publication series raw materials Nr. 1998/07. 2. [Alkemade et al 1996] Alkemade, J.R.M.; Wiertz, J.; Latour, J.B.; kalibratie van Ellenbergs milieuindicatiegetallen aan werkelijk gemeten bodemfactoren. Rapport 711901016; RIVM, Bilthoven 1996. 3. [Bakker and van de Meent 1997] Bakker, J. en van de Meent, D. ,Receptuur voor de berekening van de Indicator Effecten Toxische Stoffen (Itox), RIVM rapportnr. 607504003, RIVM Bilthoven, juni 1997. 4. [Meent et al 1999] Quantifying Toxic Stress in LCA by means of Potentially Affected Fraction (PAF) Dik van de Meent 1 , Mark J. Goedkoop 2 and Anton M. Breure 1 1 RIVM Laboratory of Ecotoxicology, PO Box 1, 3720 BA Bilthoven; and 2 PRé Consultants, Plotterweg 12, Amersfoort, The Netherlands (to be published) 5. [Hamers et al 1996] Hamers, T., T. Aldenberg, T. & D. van de Meent (1996) Definition report -Indicator Effects Toxic Substances (Itox). RIVM report number 607128001. 4. [Zwart and van de Meent 1998] Van de Meent, D. & D. de Zwart (1998) Potentially Affected Fraction of species as indicator of Toxic Stress on Ecosystems. In: Probabilistic Risk Assessment: New Approaches for Pesticides and the Environment, A. Hart, N. Mackay, K. Solomon (eds.). In press.

Methodological Range:

Geographical range is Europe Data are based on hierarchist perspective

Notes:

Existing Characterisation Factors of Ecotoxic substances soil emissions impact on PDF

Characterisation Parameter

Category Indicator

Impact Indication Principle

Aspect

Substance

Quantity

Unit

Notes

CFactor

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