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Characterisation Method Information

Characterisation Method Name:

Contributions to EF(etsc) via emissions to soil

Version:

1997

Date Completed:

1997

Principal Method Name:

EDIP: chronic eco-toxicity in soil

Method Description:

Chemicals emitted as a consequence of human activities contribute to ecotoxicity if they affect the function and structure of the ecosystems by exerting toxic effects on the organisms which live in them. If the concentrations of environmentally hazardous substances caused by the emission are high enough, the toxic effects can occur as soon as the substances are released. This form of toxic effect is called acute ecotoxicity. It often results in the death of organisms exposed.
Toxic effects which are not acutely lethal and which first appear after repeated or long-term exposure to the substance are called chronic ecotoxicity. Chronic ecotoxicity is often caused by substances which have a low degradability in the environment and which can therefore remain for a long time after their emission (persistent substances). Some substances
also have a tendency to accumulate in living orga nisms, so that tissues and organs can be exposed to concentrations of the substance which are far higher than the concentrations in the surrounding environment. The chronic ecotoxicity of a compound is thus determined by its toxicity, its biodegradability and its ability to accumulate in living organisms. The
result of a chronic ecotoxic impact can, for example, be reduced reproductive capacity, which means that the species' chances of survival in the longer term are reduced.
Ecotoxicity is an impact which predominantly affects the environment on local and regional scales. It can be a global impact for some toxic substances of very low biodegradability with a strong tendency to accumulate in living organisms.

Ecotoxic impacts can involve many different mechanisms, with the common feature that they all result in direct toxic impacts on ecosystems.
Compared with the other environmental impact categories, ecotoxicity thus has the character of a composite category which includes all substances from the inventory which can have a direct effect on the health
of the ecosystems. The list of substances classified as contributing to ecotoxicity will therefore be much more comprehensive than the corresponding lists of the other environmental impacts, and it will include
many different types of substances with widely differing chemical characteristics.

The procedure for determining whether a compound should be regarded as contributing to ecotoxicity, and for calculating the ecotoxicity potentials, is given below.
An attempt has been made to make the method simple to use, and to fix the framework as far as possible. Nevertheless, some chemical and ecotoxicological background knowledge is required to use the method.

1 Determine which substances contribute to
ecotoxicity

For a substance to be regarded as contributing to ecotoxicity, it must be toxic to organisms in the environment or to the way in which the interact in the ecosystem, i.e. to the ecosystem's structure and function. Determination of which substances to include cannot be based solely on the substances' toxicity. The chronic toxicity which can be evident after long-term exposure to the substance is also influenced by the persistence and the ability of the substance to accumulate in living organisms.
The chemical hazard screening method therefore focuses on the following characteristics of a substance:

• The substance's ecotoxicity, which is determined experimentally in ecotoxicity tests.
• The substance's persistence, which is determined experimentally in tests of its biodegradability.
• The substance's potential for bioconcentration, which is determined
directly in experiments or estimated on the basis of its octanol-water partitioning ratio, Pow which is used as an indicator of the substance's tendency to accumulate in adipose tissue.

2 Calculate the ecotoxicity potential

As for nutrient enrichment and acidification, there is no internationally
accepted set of equivalency factors expressing substances' potential toxicity in the environment in a way which can be used in the calculation of potentials for ecotoxicity. There are various proposals for how ecotoxicity can be handled in the LCA, but in the authors' view, their scientific
foundation is too weak, or their demands on data are too high to make them operational and usable in practice. It has therefore been necessary in the EDIP program to develop a method for calculation of the ecotoxicity potentials of emissions. The EDIP method is inspired by the EU
Commission's technical guidelines for risk assessment of chemicals in the environment (European Commission, 1996). It has been presented several times at conferences and workshops in SETAC (Society of Environmental Toxicology and Chemistry)(Wenzel & Hauschild, 1993; Hauschild et aL, 1993; Hauschild, 1994), and has entered into the methodological discussions in SETAC.

EP(et) is the ecotoxicity potential in one of the environmental compartments, water, soil and sewage treatment plant, determined as the product of the quantity of substance Q emitted and the equivalency factor EF for
the emission regarding the compartment in question. The ecotoxicity potential is measured in cubic metres (m3) of the compartment. It corresponds to the volume of the compartment to which the emission should
be diluted in order to obtain a concentration of substance so low that no ecotoxic effects would be expected from the emission.

The equivalency factors listed in the right side are determined as the product of three factors which represent the substance’s dispersion in the environment, its ecotoxicological characteristics 1and its
biodegradability. To calculate the equivalency factors it is therefore first necessary to

• Determine the fraction (f) of the emis
which reaches the different environmental
compartments after dispersion, such as fwa which is the factor between water and air compartments.

• Calculate ecotoxicity factors (ETF) representing the substnnce's potential ecotoxicity in the three compartments.

• Determine the biodegradability factor (BIO)for the substance

The equivalency factors for ecotoxicity depend exclusively on the characteristics of the substance. Those will be the same independently of the context in which the emission occurs. It is therefore necessary to calculate them only once for each substance. The factors calculated can be reused every time the substance appears in an inventory to be assessed.

2.1 Determine the fraction 'f of the emission which ends in the different compartments

The inventory may include emissions to water, air and soil. Even if a substance is emitted to one compartment, e.g. air, it may well contribute primarily to the ecotoxicity potential in another compartment.
Redistribution calculations decide:
• For which parts of the environment ecotoxicity potentials are to be calculated.
• The quantity of substance contributing to the ecotoxicity potential in each of the compartments.
For each individual emission, the redistribution calculations result in distribution factors fs and fw, which specify for how large a fraction of the
emission ecotoxicity potentials should be calculated in the compartments soil and water.

The redistribution calculations in the EDIP tool are simple and modest in their data requirements. The method was designed to ensure that the redistribution calculations can be done for all substances in the inventory.

2.1.1 Substance emitted to the air compartment

A substance emitted to air can be deposited to the water and soil compartments if it is sufficiently stable, i.e. if it is not broken down in the atmosphere first. As a rule of thumb, the EDIP method assumes that
deposition occurs only if the substance's half-life in the atmosphere exceeds 1 day.
If the substance is thus deposited, it can contribute to chronic ecotoxicity in water or soil, but it is unlikely that substances deposited from air can cause acute ecotoxicity in water, fwa is therefore set to 0.

On deposition, the substance is distribibuted
between the water and soil compartments in the rario a: (I-a). The magnitude of 'a' should be fixed as that part of the area of deposition of the emission which is water, 'a' can be fixed for conditions
representative of the region in question.
A substance deposited from air is assumed not
to re-evaporate from the water or soil compartment, even if it is volatile. The distribution factors thus describe the final distribution of the substance.

As no ecotoxicity potentials are calculate for ecosystems in the air compartment, the substance does not contribute to any ecotoxicity potential if it is emitted to air and has a half-life of less than 1 day.

2.1.2 Substance emitted to the water compartment

Even if a substance is emitted with waste water, it may well evaporate to
the air compartment. Even quite volatile substances may, however, remain in the recipient long enough to cause acute ecotoxicity; fwa should therefore be set to 1 in all cases of emissions to the water compartment.
The substance's volatility from water is described by its Henry's law
constant H, and as a rule of thumb it is assumed that if H > 1E-03 atm • mVmol, the substance will evaporate from water. In this case it is assumed that the entire quantity emitted will evaporate.
From the air compartment, the substance may deposit to water and soil, as described for substances emitted to the air compartment, provided that the substance is sufficiently stable not to be broken down first.

2.1.3 substance emitted to the soil compartment

A substance can be emitted to soil either directly, e.g. by spraying of cultivated land with pesticides, or indirectly, e.g. through the spreading of sewage sludge. If the substance is volatile it can evaporate and possibly deposit again to the soil and water compartments in the same way as
described for substances emitted to the water compartment.

2.2 Calculate ecotoxicity factor, ETF

For all compartments, the expression for the ecotoxicity factor is defined as the fraction with an ecotoxicity effect concentration in the denominator. For the compartments water and soil, the substance's PNEC value is used. PNEC stands for Predicted No Effect Concentration, i.e. the
concentration predicted to have no ecotoxic
effects in the compartment.
For sewage treatment plants, the ecotoxicity
concentration is the substance's LOEC value for aerobic heterotrophic bacteria. LOEC stands for Lowest Observed Effect Concentration, i.e. the lowest concentration which in an ecotoxicity test shows toxic effects in this case on the group of
bacteria called aerobic heterotrophs.

2.2.1 Estimate PNECwc

It will normally only be possible to find laboratory data for a substance's ecotoxicity. In the laboratory tests, selected test organisms have been exposed to the substance under standardized conditions for a shorter or longer time.
In a short-term laboratory test (acute ecotoxicity test), that concentration of the substance which kills e.g. 50% of the test organisms (LC50, Lethal Concentration 50%) is determined.
For ecotoxicity tests of longer duration (chronic ecotoxicity tests), the highest concentration of substance which produces no observed effects on the test organisms (NOEC, No Observed Effect Concentration) or
the lowest concentration which has resulted in observed effects (LOEC) is most often reported.
For LCgo, NOEC and LOEC values, the higher the value, the less toxic the substance.

PNEC, the concentration of substance found
to have no toxic effect in the environment, is determined on the basis of the results of laboratory tests, i.e. LC50, NOEC and LOEC values. The quality and the relevance of the available toxicity
tests is assessed, and on this basis an assessment factor is established which, on division into the lowest of the ecotoxicity concentrations used, gives the PNEC value for the substance. Even if an attempt has been made to standardize the procedure for determination of PNEC values and to simplify it relative to a traditional hazard assessment, expert judgment will often be
required. Some background in ecotoxicology is
generally needed to determine the assessment factors.
This point is illustrated in the following example.

2.2.1.1 Correction for the substance's capacity for bioconcentration

Any capacity of the substance for accumulation in living organisms will
be able to increase its toxicity in chronic laboratory tests where the exposure lasts long enough for the bioconcentration to have time to occur in the test organisms. If the estimation of PNEC, is based on the results of chronic ecotoxicity tests, the value found will therefore also reflect the
compound's bioconcentration potential.
Among organic compounds, it is generally only the highly fat-soluble
substances which bioconcentrate. As a rule of thumb, the substance's Pow should be over 1000.

If PNEC, for a substance which can bioconcentrate is estimated on the basis of data for acute ecotoxicity, the bioconcentration potential will not be represented in the resulting PNEC value. In this case the PNECwc value found may require correction for the substance's bioconcentration potential. Hauschild et al. (1997a) discuss how a decision is made on whether this is the case and how the PNEC value should then be corrected.

2.2.2 Estimate PNECwa

For acute ecotoxicity, the procedure for determination of the concentration of substance which is not expected to have any effects in the environment is the same as described for chronic ecotoxicity.

Estimation of PNECwa is based on data for acute toxicity, and the assessment factors are lower by a factor of 10.

2.2.3 Estimate PNECsc

In principle, determination of PNEC for chronic terrestrial ecotoxicity
follows the method presented for chronic aquatic ecotoxicity. It is, however, a problem that studies of ecotoxicity on soil-dwelling organisms have been undertaken for very few compounds only. In practice it is
therefore almost never possible to base the calculation of a PNEC value for soil on data for soil-dwelling organisms. Data on the substance's ecotoxicity to aquatic organisms is instead used as an approximation. A correction is made for the difference in the substance's availability to organisms in water and soil. This is a generally used procedure in the environmental hazard assessment of chemicals in soil.
The correction for the reduced bioavailability is made by multiplying
PNECwc by (Kd + 0.27). Kd is the substance's coefficient of adsorption in soil, i.e. the ratio of the concentration of the substance on soil particles to the concentration in the soil's liquid phase. The value 0.27 is the average relative water content of soil (1 water/kg dry matter soil).
If it is not possible to find some other value for K, it can be estimated for nonionic organic compounds as Kd ~ 0.02 • Pow
By multiplying by the soil's dry density of 1.5 kg/I, PNECsc is expressed as a volumetric concentration similarly to the PNEC values for the other environmental compartments.
The procedure for determination of PNECsc on the basis of ecotoxicity data for aquatic organisms can be illustrated by continuing the example of n-butyl acetate:

2.3 Determine the biodegrability factor, BIO

The biodegradability factor represents the substance's biodegradability:
the less the biodegradability, the greater the factor. Determination of BIO requires some knowledge of the biodegradability tests and of the tests which have been carried out on the substance.

2.4 Calculate equivalency factors

Calculate equivalency factors as:

EF(etwa)=fwa*ETFwa
EF(etwc)=fwc*ETFwc*BIO
EF(etsc)=fsc*ETFsc*BIO
EF(etp)=ETFp

The factors in the expressions are described above, and the equivalency factors can now be calculated for the ecotoxicity potential in the different environmental compartments

2.5 Calculate ecotoxicity prtentials

EP(etwa)=Q*fwa*ETFwa
EP(etwc)=Q*fwc*ETFwc*BIO
EP(etsc)=Q*fsc*ETFsc*BIO
EP(etp)=Q*ETFp

When the equivalency factors have been calculated for the different compartments, the ecotoxicity potentials can be determined as the product of the quantity of substance emitted, Q, and the associated equivalency factors. If the emission has passed through a sewage treatment plant, an ecotoxicity potential is calculated for the plant for the quantity which was discharged to it.

Literature Reference:

Henrik Wenzel, Michael Hauschild and Leo Alting (1997 ): Environmental assessment of products Vol. 1 Methodology, tools and case studies in product development London Chapman & Hall

Methodological Range:

Geographical range is Europe

Notes:

Existing Characterisation Factors of Contributions to EF(etsc) via emissions to soil

Characterisation Parameter

Category Indicator

Impact Indication Principle

Aspect

Substance

Quantity

Unit

Notes

CFactor

EF(etsc)