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Danish experience. Best Available Techniques – BAT - in the clothing and textile industry

Annex A
Score System for Sorting of Chemicals

Summary

The score system is an administrative method of sorting chemicals on the basis of information especially from the chemical supplier's specification sheets. The sorting permits a priority selection of chemicals which, because of actual consumption and information on environmental behaviour, should be subject to closer examination.

The score system is based on the parameters usually considered to be the most interesting in connection with characterisation of substances injurious to the environment of industrial sewage. The parameter A is a score on the estimated amount of chemical, which is discharged into the environment as wastewater. B is a score on biodegradability, and C is a score on bioaccumulation. The structure of the score system appears from the table in chapter 2.

Together, A, B and C indicate the potential presence of the substance in the environment; (exposure); how much of, how long and how is the substance present in the aquatic environment. A influences the effect of B and C, while B influences the effect of C. The total score, which is obtained by multiplying the score for A, B and C, is called the exposure score.

Effects of chemical exposure depend on the toxicity of the chemical. The toxicity (D) should be evaluated concurrently in proportion to the exposure.

Each parameter is given a numerical value between 1 and 4 with 4 indicating the most critical environmental impact. Missing information involves highest score. The result is that each substance can be given a score as to exposure (A´ B´ C), and independent of this, a score as to toxicity (D). Subsequently, it will be possible to make a ranking of the chemicals.

Application of the system implies that the system is worked into the wastewater permits or environmental approvals of the companies. Hereafter, the companies should send in information on consumption of chemicals as well as environmental data. The first time, information on all chemicals employed should be submitted, but following, reporting of new chemicals may take place concurrently with the employment of these. At least once a year, the statement of consumption should be updated.

The Federation of Danish Textile and Clothing Industries is prepared to act as "consultant" for the individual companies, and it has established a data base management system for storing of information on chemicals and calculation of score. By means of the data base facilities, it will thus be possible to print out a list of the employed chemicals and the calculated score (a Score Report) specifically for each company. This list could subsequently be supplemented with a detailed analysis of the chemicals, which were given a high score.

The information now available should form the basis of the environmental authority's (municipality/county) evaluation as to possible "interventions".

2. Description of the score system

The score system is based on the parameters usually considered to be the most interesting in connection with characterisation of substances injurious to the environment of industrial sewage:

A Discharged amount of substance
B Biodegradability
C Bioaccumulation
D Toxicity

The structure of the score system appears from the tables overleaf.

Together the parameters A, B and C indicate the potential presence of the substance (exposure) in the environment; how much of, how long and how is the substance present in the aquatic environment. A influences the effect of B and C, while B influences the effect of C. Thus, the total "exposure score" is obtained by multiplying A, B and C.

As regards mixtures of substances solely consisting of inorganic compounds, the parameter "biodegradability" is without meaning. A calculation of the "exposure score" A´ B´ C is thus not relevant to such substances/mixtures.

The effect of the presence of a substance in the environment depends on its toxicity. The toxicity score should be evaluated concurrently and independently in proportion to the exposure score.

Each parameter is given a numerical value between 1 and 4 with 4 indicating the most critical environmental impact. Missing information involves highest score. The result is that each substance can be given a score as to exposure (A´ B´ C), and independent of this, a score as to toxicity (D). Subsequently, it will be possible to make a ranking of the chemicals.

Data Quality

It is advisable that the data used as score basis as far as possible have been obtained according to internationally approved methods of examination. Appendix 1 is a list of methods of examination, which are considered approved.

Within the parameters B and C and D, data on different levels are used. The highest level represents data generated on basis of examination conditions, which seen in proportion to data from lower levels are most comparable with a natural aquatic environment. As regards the parameter C, data obtained from standardised bioaccumulation tests with fish are thus more realistic than data from examinations based on determination of the distribution of the substance in a two-phased mixture of octanol and water (P_ow-data). However, P_ow has a more direct correlation with bioaccumulation than solubility data.

The highest level is stated at the top within each parameter. When preparing the score system, it has been taken into consideration that when data from the lowest quality level are used, the certainty will be less.

It is a prerequisite that data on the highest available level should always be used.

In order to secure the practical execution of the C score, it has been necessary to accept that the score can be established on the basis of qualitative information on solubility. With this end in view, there has been prepared a "diagram for establishment of the C score on the basis of qualitative information on solubility" (appendix 2) (enclosed).

Exposure score (A ´ B ´ C)

Toxity score (D)

Application of the score system is described in chapter 3.

3. Guidelines to the score system

3.1 Discharged Amount of Substance (A)

The discharged amount of substance is the difference between the amount of chemical used cf. the stock list, and the part, which is expected retained in the textile. As to dyestuffs, the retention ability in the textile (the percentage of utilisation) is relatively high, whereas it is very poor, probably about 0%, as to accessory agents such as detergents.

If possible, accessory agents, which are converted in connection with the process, are to be scored on the basis of information of the conversion product. If no information is available, the substance is scored on the basis of the starting substance with a percentage of utilisation of 0, if no other percentage of utilisation has been detected/calculated.

As to dyestuffs, the following percentages of utilisation are presumed, if no further information is available:

If the percentage of utilisation is stated as ">" x%, the actual utilisation rate is presumed to be x%.

The basis for the used percentages of utilisation is to be accepted by the surveillance authority.

If the physical/chemical qualities of the chemical related to the application method indicate a considerable outlet to the air, this should be set off in the calculated amount discharged with the wastewater. The basis for calculation of outlet to the air is to be accepted by the surveillance authority.

As to companies connected to a municipal sewage plant, A is initially calculated as starting point in proportion to the discharge to the public sewage system.

As to companies having a separate discharge of sewage, A is also initially calculated as starting point with reference to inlet of the sewage plant. If a specific documentation for removal in the sewage plant is available, this has to be taken into consideration when calculating the discharged amount.

The consumption of chemicals can be scored on basis of either the weekly or the annual consumption. Other periods of consumption (< 1 year) can be estimated by a simple conversion from the actual period into weeks.

If the consumption pattern for a substance is distinctly periodical, the consumption should in principle be scored on a weekly basis, as this will then give a more correct picture of the impact. This is especially important when calculating the D-score.

When calculating the score for new substances in the production, it will often be best to fix the amount score on basis of an expected weekly consumption. This is due to the fact that it will probably be impossible to predict the annual consumption.

In case of an experimental consumption, a weekly consumption will also be most relevant.

Information on consumption figures of products containing several substances is as a starting point stated on basis of the total product amount notwithstanding that the "active" chemical only represents a small part of the product amount. The score figure could possibly be accompanied by a note.

3.2. Biodegradability (B)

The criteria making the basis of the score are primarily the biodegradability of a substance in surface water or under more favourable conditions in sludge.

If a substance is decomposed or eliminated by a non-biological process this information will be correspondingly relevant, and after a more detailed examination, it will be possible to include it in the score (cf. below on eliminability).

The biodegradability of a substance can be described according to different degradation levels:

1. Primary biodegradability, which means that the substance loses its chemical identity.
     
2. Functional biodegradability, which means that a specific quality of the substance disappears.
     
3. Total biodegradability, which means a complete conversion into carbon dioxide, water and other inorganic compounds.
      
4. A complete mineralization, corresponding to c), but where the inorganic compounds are found as oxides.

The test methods, which are approved for determination of the biodegradability of a substance imply that the degradation of the substance is measured in relation to a total degradation, corresponding to item c).

Information on degradability is stated according to 3 different test levels:

Degradability in recipient water:

This degradability test is to refer to tests giving relatively poor conditions for biological degradation; i.e. not adapted test culture, low biomass and a relatively high concentration of the test substance, The degradation is to start before 28 days.

Different principles according to approved methods are used. It is common for all methods that the test substance is the only carbon source.

The results are stated as a % degradation after a fixed test period. If biodegradability data are only stated as intervals, "50-100%" is used synonymously with ">60%". This is stated in brackets after ">60" in the score system.

Degradability in sludge

Degradability in sludge is to refer to tests giving relatively good conditions for biological degradation; i.e. a very large bacterial density and a high concentration of the test substance. Furthermore, the tests can be made with a longer exposure time, which secures better possibilities for adaptation. Active sludge is used as inoculum.

BOD/COD-conditions

This parameter may only be used in cases where data from degradability tests are not available. BOD refers to the biological oxygen consumption after 5 days. COD is the chemical oxygen consumption.

Eliminability

A substance can be eliminated from the water phase by degradation, sorption or evaporation. The concept "eliminability" covers all 3 of the processes. Some data sheets only list information on eliminability. Determination of the score on basis of information on eliminability can take place according to the "scale" for "degradability in sludge cultures".

Degradability of mixtures of substances

Degradability of products, which are mixtures of several substances, should in principle be estimated in relation to each individual substance. If such information is not available, the score is made on basis of the stated degradability of the product supplemented with a note indicating that it is a mixed product.

3.3. Bioaccumulability (C)

The bioconcentration factor (BCF) conveys for a given substance and a given aquatic organism the relation between the concentration of the substance in the organism and the water phase, i.e. the tendency of the substance to accumulation in organic tissue.

Bioconcentration data can be obtained on 3 "levels". The highest level is a direct determination by tests on fish. The medium level is a determination of the distribution ratio of the substance in an octanol-water "mixture". This ratio is described by a distribution coefficient called P_ow.

The lowest level is based on information on solubility (C_s, measured or estimated).

The assessment of bioaccumulability according to the lower levels is based on basis of the correlation existing between BCF and P_ow or C_s.

It has been proved in /8/ that the presumed correlation between P_ow and BCF disregards the fact that the possibility of a substance for bioaccumulation in tissue will be strongly limited for substances which have an extremely low fat and water solubility (e.g. pigment dyestuffs).

The same is in evidence as to large-molecular compounds (actually the steric configuration) where the molecular size can constitute a barrier to the possible absorption through cell membranes.

In order to obviate the above limitations, the score system has been drawn up with 3 subscales (C1, C2 and C3) for biodegradability. The molar weight (MW) of the chemical is decisive for what sub-scale one should use.

For chemicals with MW > 1000 g/mol the score figure is fixed to be 1 unless information on stable degradation products with MW < 1 000g/mol, or research indicating that the substance is bioaccumulated is available.

The working group has decided, that if exact information corresponding to the conditions for C1, C2 or C3 is not available, the score can temporarily be made on basis of qualitative information on solubility (dispersing ability, miscibility, emulsion etc.). Qualitative information is interpreted in accordance with the diagram in appendix 2.

Products containing several substances are scored according to the same principles, which apply to the B-score.

3.4 Toxicity (D)

The D-score is fixed in relation to the difference between the concentration which gives a toxic effect, and the concentration which is calculable to be found in the waste water.

The score can be calculated according to different conditions. It is thus important that the score is not stated without reference to the conditions.

The concentration in wastewater can be considered from two points of view:

The average concentration which refers to the annual loss of chemical to the wastewater divided by the annual water volume consumption. As to a substance, which is used steadily throughout the total calculation period, the actual wastewater concentration will be reasonably described by calculation of the average concentration. As to substances, which are used for short campaigns, the average concentration will "underestimate" the actual wastewater concentration.

The extreme concentration which refers to the annual chemical loss to the wastewater divided by 24 hours' water volume consumption.

Two different test categories are considered:

Test on fresh-water fauna or on algae, e.g. acute toxicity in fresh-water fish, crayfish or microalgae. The result should be stated as LC0 (algae test EC0), which is the highest concentration that does not give any toxic effect.     In cases where only LC50, is available, it is possible in the case of LC50 ~ 100 mg/l to convert from LC50, to LC0 by dividing by 3. In the case of LC50>100 mg/l, no conversion is made.

Test on sludge culture. The effect concentration (EC20 in sludge organisms, either activated sludge or Pseudomonas putida, a bacterium which can be found in wastewater treatment plant sludge.

According to the above, the different conditions can be placed together in 4 combination possibilities stated as D1, D2, D3 and D4.

D1 and D2 represent data on higher quality levels than D3 and D4.

D-score for different substances are only comparable within the same data level.

As it appears from the score system, the toxicity should be measured concurrently in relation to the exposure. If the actual consumption pattern is best described as periodical, D2 or D4 should be basis for the assessment.

In general, a low score in D2 or D4 may indicate that the toxicity is of secondary importance in relation to the exposure score.

4. Comments to the score parameters

It should be noted that the score system should not be used to inorganic compounds. These substances should primarily be assessed on basis of a toxicity criterion related to the amount discharged.

Amount

The score levels 1 - 4 have been fixed on the basis of the consumption pattern in 1987 so that "1 " reflects a small consumption, whereas "4" reflects a big consumption.

The levels 1 - 4 should possibly be revised concurrently with changes of the raw materials consumption of the company.

When calculating the discharged amount, a deduction of the part which is removed in the sewage plant should in principle be made. In practise, however, sufficient documentation of the degrees of treatment in the sewage plant are usually not yet available. Therefore, an approved basis for making any deduction for removal in the sewage plant is still not available.

One cannot preclude that different trade names cover products which are approximately identical as regards the chemical composition. It is not the intention that the A-score is minimised by deliberately using such alternative products. In principle, these product groups should be pooled to a common A-score.

Degradability - Surface Water

A substance is described as "readily degradable" if the degradation results in an elimination of 70% of the resolved organic carbon, 60% of the theoretic oxygen consumption or formation of 60% of the theoretic quantity of carbon dioxide. Moreover, the substance is considered to be readily degradable if other scientifically well-researched tests have shown that the substance is decomposed biologically or non-biologically to a level > 70%. The degradation is to take place within 1 0 days of a 28 days' test period.

To avoid more score levels and a sharp distinction between choice of method, 60% has been chosen as a general limit.

Most of the data sheets state biodegradability according to the intervals < 10%, 10-25% and 50-100%. By means of the applied intervals for the degradation score it will therefore not be possible to give a lower score than "2". This is, however, in bad accordance with the intentions to secure that unproblematic substances are sorted out. The chosen "alternative", score 1 at 50-100", is therefore a reasonable compromise.

If degradation data based an proper degradation tests are not available, the quantity BOD/COD > 0.5 can be applied as criterion for easy degradation /14/. Compared to the 1st edition of the score system, there has been made a change of the score scale for the BOD/COD criterion. The lowest score has been changed from 1 to 2. This is due to the principle that there must be accordance between data quality and "certainty" (see page 3). In the first edition there thus was a disproportion between the score according to the sludge test and the score according to BOD/COD.

It should be noted that data sheets generally state the degradability of a compound product (mixture of substances) as the sum of the degradability of the single components multiplied by the proportional part with which the component enters into the compound. Inorganic components are estimated to be 100% decomposable.

Scoring on basis of "product" information implies a risk to "overlook" the presence of non-degradable or not readily decomposable substances, which form part of products. This risk is partly neutralised by the fact that the amount score has been fixed on basis of the total amount of the product compound.

Degradability - Sludge

Tests based on degradation in sludge cultures are not comparable with the proportions in the recipient. In principle, the tests can only be applied to predict the indegradability of a substance, but not its possible degradability in the recipient.

Substances which are decomposed by less than 20% by using methods based on sludge culture, are considered to be "not readily decomposable or slowly decomposable", and they are often described as persistent. Substances, which are decomposed by more than 70% are described as "potentially decomposable" (inherent biodegradability). Substances, which are decomposed by between 20% and 70%, are generally considered to be decomposable, but it is likely that there will be generated stable metabolites by this degradation.

It is not possible to "interpret" degradability in surface water exactly to degradability in sludge culture. One can only establish that the degradation in sludge will usually be bigger than the degradation in the water phase. This is reflected in the chosen levels of the score.

Bioaccumulability

/10/ has put forward some criteria as to when bioaccumulation tests with fish should be considered unnecessary:

	Pigments which have a very poor solubility in both the water phase (Cs < 0.1 mg/l) and the organic phase (Cs <10 mg/l) are considered to be "non- accumulative".
	Dyestuffs, which are highly water-soluble (Cs > 2 g/l), are supposed to have so little affinity to biological tissue that they are considered to be "non-accumulative".
	Dyestuffs having a molecular weight (MW) higher than 450 g/mol and a cross section bigger than 1.05 nm are supposed to be too bulky to be absorbed into biological tissue. The consideration is "little probability of accumulability".

The molecular weight is the most simple parameter describing the molecular size. In general, information on more directly describing parameters will not be available.

A score system proposed by the Nordic Council of Ministers (MST-environment project 153, 1990) suggests that MW = 1000 g/mol is used as limit for bio-accessibility, and uses the character as a score parameter together with e.g. bioaccumulation at P_ow-value and degradability.

Chemicals with a Molecular Weight higher than 1000 g/mol

On basis of the information that large molecules will most probably not be bio-accessible, it is reasonable to sort out big dyestuff molecules, which usually represent very molecular weight stable molecules. Possible changes of the radical structure will be of small importance for the size of the molecule. By choosing MW = 1000 g/mol as limit for this sorting, there is accordance with the Nordic Council of Ministers' score system. At the same time there is a good margin to the limit of 450 g/mol proposed by /10/. However, it should be noted that /10/ connects the molar weight criterion with molecular cross section and fat-solubility etc.

In fact, the precondition to "acquit" chemicals with a molecular weight of more than 1 000 g/mol is that no stable products of decomposition with accumulative qualities are generated during a possible degradation. Often, this information will not be available. To make the system operative, the criterion "unless information on stable degradation products with a MW < 1000.

The probability that bioaceumulation data from tests on fish are available is little. If so, the substance is to be evaluated on basis of these data.

Chemicals with a Molecular Weight between 1000 and 500 g/mol

The probability that the chemical is bio-accessible is small. It is, however, bigger than it is the case for the above group.

The probability that bioaccumulation data from tests on fish are available is little, cf. the priority proposed in /10/.

It is an accepted fact that the critical BCF-value is 100. It is among other things applied in the EC Commission's proposal for classification and marking of substances harmful to the environment.

As to P_ow data, the critical value has been fixed on basis of the theory that if P_ow < 1000, then the BCF will be < 100 /7/. This quantity is recommended as criterion as to whether it is recommended to make accumulation tests on fish.

The grading for P_ow > 1000 is rather gentle as the molecule size only gives little probability of accumulation. However, compared with the score for amount and biodegradability, the grading secures that the substance will be taken into consideration, if the substance is not easily degradable, and is used to a considerable extent.

As to solubility data, the critical values have been fixed on the basis in 1101 and the mathematical connection between solubility and P(ow). It is possible to obtain a higher score than it is the case for P_ow data on the background that "solubility" is a weaker parameter than P_ow.

Chemicals with a Molecular Weight smaller than 500 g/mol

In this group most of the data are expected to come from accumulative tests on fish. The grading of the score for BCF-data is identical with the above score module.

As regards P_ow data, the same critical value as mentioned above is applied, but P_ow > 1000 is evaluated on a par with BCF > 100. In these cases, there is a considerable indication of bioaccumulation.

As to solubility data, the critical values have been made more stringent. Roughly, the same classification as proposed in the original score system /2/ has been applied.

Toxicity

The toxicity of composite wastewater is notoriously difficult to characterise on basis of the information on the single substances. The reason is that the effect from the coexistence of the substances often cause that toxicity of the single substances cannot be considered as additive. Some substances may react mutually, and by this, the toxicity may be reduced or possibly increased.

Thus, the toxicity should above all be controlled by a "whole effluent" toxicity control and by establishment of a fixed permit limit regarding the total toxicity of the wastewater. By this, possible synergistic effects would be included.

Information on the toxicity of the individual substances is, however, still relevant, as this information can at least be used for a guideline estimation of the potential contribution of a substance to the toxicity of the wastewater. It will always be desirable to avoid using toxic substances. The score renders potentially problematic substances visible.

In general, treatment in sewage plants will be able to reduce the toxicity of the wastewater either as a result of a degradation of the substances or because of the retention in sludge. The actual reduction can only be determined on basis of toxicity tests on corresponding samples of head water, sewage water and sludge from the sewage plant in question.

The basis for the conversion from LC₅₀ to LC₀ by dividing by 3 are experience figures (The Water Quality lnstitute). The conversion is in reasonable accordance with EPA's "Criteria Maximum Concentration", which is defined as 0,3 times the lowest LC₅₀ value for acute toxicity towards at least 3 species. /16/.

As regards LC₅₀ >100 mg/l no conversion is made. The reason is that many toxicity tests cannot be continued beyond the concentration 100 mg/l. If ">100" is used as "absolute 100" there will therefore in most cases occur a distorted weighting of the result in connection with a possible conversion (division by 3) to LC₀.

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