Survey of azo-colorants in Denmark

Conclusion and Recommendation

Conclusions on the individual elements of the survey

Mass balance

In order to establish the mass balance of azo colorants in Denmark, it has been a prerequisite to base the estimations on assumptions. The number of assumptions means that the mass balance does not show the precise flow of azo colorants in Denmark, but at present, it is the best estimate for the total flow of colorants.

It is concluded that the results of the present survey may indicate the order of magnitude of the mass balance but not the exact figures/amounts.

Azo colorants may be subdivided in two groups: dyes and pigments. When looking into the ratio of consumption and use between the two groups of azo colorants, pigments clearly dominate the use of azo colorants in Denmark. They constitute approximately 66% of the colorants used and contained in imported products. Pigments are used in all industrial trades included in the survey. Pigments are also produced in Denmark, and it is assumed that the production amounts to approximately 18,000 tonnes p.a., and that approximately 90% are exported.

The survey indicates that dyes are, in contrast to pigments, almost exclusively used in the textile industry and is imported within textile products. The latter dominates and constitutes almost 75% of the total dye input to Denmark. However, it should be noted, that azo dyes may be used to a lesser extent in other industrial sectors. There is no direct production of dyes in Denmark, but several mixing houses manufacture dye formulations by the blending of different dyes.

It is concluded that pigments constitute the most significant part of the flow of colorants in Denmark, but at the same time, azo dyes constitute an important part (34%). Dyes are mainly associated with textiles but are used in other products/trades too. Thus, it is possible to distinguish between the two groups of azo colorants: pigments and dyes in the mass balance, and allocate their consumption and use among trades. However, based on the present findings it is not possible to qualify the distribution of the different technical (chemical) groups of dyes, except for textile and pigments. In addition, it is not possible to conclude on the consumption and use of individual azo colorants.

Because of the large number of more than 3,000 azo colorants, , the survey focused on colorants which according to the literature are in general use. Therefore, the individual colorants encompassed in the survey are not totally representative of the colorants used in Denmark.

The survey revealed that the major importers and manufacturers of azo colorants do not import or sell colorants, which are subject to restrictions in e.g. Germany. However, the restricted compounds may be present in textiles and leather products from e.g. Asia, Eastern Europe and South America. The imports from Asia alone account for 430 tonnes of azo dyes, primarily in textiles, and 40 tonnes of azo pigments in leather products. Thus, at least 20% of the azo dyes associated with imported goods, stem from regions where there may be a potential use of the restricted dyes. But it should be noted, that the possible content of problematic dyes and their cleavage products in imported goods has not been assessed, and whether the goods contain these dyes or not or to which degree is not known.

It is concluded that dyes contained in imported products, mainly textiles and leather, may contribute to a flow of azo dyes based on potentially carcinogenic aromatic amines in Denmark.

The survey indicates that the problematic azo dyes are being out-phased at least for the major manufacturers. Furthermore, there is world-wide a trend towards increased use of pigments and a decline in the use of dyes. The azo dyes are cheap but have relatively poor technical properties, e.g. light fastness, etc. Therefore, it may be speculated if there besides a general trend towards an increased use of pigments may be a market trend towards use of other chemical classes of colorants than azo colorants.

Dyes released to waste water constitute 6% of the total input of dyes. More than 50% of the dyes released to waste water originate from private households. The environmental release of pigments is lower, approxi- mately 1% of the total input.

It is concluded that there is a potential release of dyes and pigments to the environment. However, in order to make any final conclusions with regards to the environmental loads, the distribution between the disposal routes, i.e. waste water, landfill and incineration as well as recycling, need to be further investigated

Human toxicity

The acute toxicity of azo dyes is low, and the acute toxicity of azo pigments is very low. However, potential health effects are recognised for the dyes. The azo linkage of azo dyes, but not of azo pigments, may undergo metabolic cleavage resulting in free component aromatic amines. At least 22 of these are recognised as possible humans carcinogens. Therefore, the toxicity of azo dyes is mainly based on the toxicity (carcinogenicity) of the component amines.

Several studies have indicated that sulphonation of the parent dye inhibits the release of aromatic amines and therefore reduces the toxicity.

It is concluded that the toxicity of the parent compounds - the azo colorants - is low, however, some of the metabolic cleavage products, e.g. 22 component aromatic amines, are potentially carcinogenic.

The potential carcinogenic aromatic amines are those containing a moiety of: aniline, benzidine, toluidine or naphthalene. They are synthesis compounds/intermediates in the manufacture of some of the azo dyes and azo pigments and are represented in all chemical classes of azo colorants. In addition, they may be present as impurities.

It is concluded that, in principle, all the chemical classes of azo colorants may represent a potential toxicological risk, if the individual colorant is synthesised from one of the 22 aforementioned aromatic amines.

In Denmark, human exposure to aromatic amines may take place as a result of a breakdown of the colorants or due to impurities of the colorants during:

	Synthesis of azo pigments.
	Manufacturing of commercial formulations.
	Industrial uses: colouring of consumer goods, e.g. plastics, textiles, leather, printing, paint and lacquer, and paper.
	Consumption by end-users of products containing azo colorants, e.g. use of paints, wearing of textiles, etc.

It is concluded that there is a small but possible risk of exposure to potential carcinogenic aromatic amines from azo colorants and coloured products in Denmark. However, to fulfil the risk assessment requires investigation of the production, manufacturing and processing technologies applied in Denmark as well as a closer examination of imported products and additional information on the content of impurities in formulations or products.

The sensitisation potential of azo colorants is rather low. However, sensitisation to azo colorants has been reported. Most reported cases, with relevance today, is related to the disperse azo dyes. Exposure to disperse dyes may take place during production of dyes and in the processing industry, predominantly textile. In addition, exposure may take place when wearing textiles, particularly those in close contact with the skin.

It is concluded that a few of the azo colorants are potentially allergenic, but it has been shown that sensitisation only is developed as a result of rather extensive exposure.

Environmental fate and toxicity

Due to the physico-chemical properties of the azo colorants, adsorption to soil and sediment is the primary fate of azo colorants in the environment, except for the ionic, acid and reactive dyes. It is indicated that biodegradation is the only degradation pathway for both dyes and their metabolites. Pigments, on the other hand, are not biodegradable.

Biodegradation of the dyes predominantly takes place in an anaerobic environment, whereas degradation of their metabolites takes place in an aerobic environment. The degradation of dyes varies from hours to several months or more, indicating that they are at least inherent biodegradable.

Substituents, like methyl, methoxy, sulpho or nitro groups reduce the biodegradability of the ionic dyes. The sulphonated metabolites may not be biodegradable either. The molecular size of the colorants may reduce the biodegradability too; this applies for e.g. disperse dyes, due to limited possibility of membrane uptake by the biota.

It is concluded that pigments and some of the dyes may accumulate in soil and sediment, due to limited bioavailability and because the prerequisite for biodegradation is the presence of an anaerobic environment. The degradation products may accumulate too, if they are not transported to the aerobic environment.

Furthermore, it is concluded that sulpho groups and other substituents may reduce the biodegradability of dyes and their metabolites. The molecular weight may reduce it too. Thus, a high degree of sulphonation and a high molecular size may, in addition, enhance the accumulation potential of the colorants and their metabolites.

With respect to bioaccumulation, it is indicated that the ionic dyes do not have a significant bioaccumulation potential in general, however, at least some acid dyes may bioaccumulate. The non-ionic dyes and pigments, on the other hand, have a high bioaccumulation potential indicated by high partition coefficients (log K_ow ). Despite the high log K_ow for pigments, experimentally assessed bioconcentration factors indicate that the immediate concern for bioaccumulation is very low. The metabolites, generally, have a potential for bioaccumulation.

It is concluded that azo colorants, with the exception of most ionic dyes, may have a potential for bioaccumulation, indicated by high partition coefficients, but due to limited bioavailability, e.g. molecular size, the bioaccumulation is generally low. The metabolites, on the other hand, have a potential of bioaccumulation.

Due to the lack of monitoring data of environmental concentrations of azo colorants in Denmark, it is not possible to validate the estimated predicted environmental concentration (PEC) with Danish data. The PEC estimates are based on the sewage treatment plant (STP) model applied in the TGD (1996) by the EU. The standard characteristics of this STP may be in accordance with the average Danish municipal STP. However, at least for industrial waste water treatment, the characteristics may not apply/corre- spond. Furthermore, the PEC estimates were carried out on the basis of the assumption that the processing industries do not carry out waste water treatment prior to outlet (PEC_{influent, stp}) which is unlikely, because most of these companies, if not all, are encompassed by a special section of the Danish Environmental Protection Law (chapter 5). Hence, their emissions are restricted and must be approved by the authorities. Subsequently, most of the companies are obliged to have some degree of waste water treatment prior to the outlet to the municipal STP. In accordance with this, the PECs have been modified "double" treatment, which reduces the PECs.

Another limitation of the PEC estimates is that all the Danish releases of colorants "are placed" in one sewage treatment plant. In order to compensate for this, the PEC_{effluent, stp} has been normalised to represent the concentration per company or per Danish inhabitant.

Based on the above mentioned modifications, the PEC_{surface water} has been estimated to be:

	0.04 to 1.44 mg/l for dye processing and use.
	0.1 to 1 mg/l for pigment production.
	0.002 to 0.4 : g/l for processing and use of pigments.

Even in this case, the PECs may be overestimated, because visual colouring of the water would be observed at levels above 1 mg/l, and the basic assumption that the degree of adsorption is in the range of 40 to 80% for dyes and 80 to 98% for pigments may be an underestimate. The size of the overestimate cannot be predicted at present.

Despite the fact of possible overestimation, the modified PECs for dyes in the aquatic environment are within the same range as concentration measures in monitoring studies abroad. However, it should be noted, that these studies, which are carried out in the US and Canada, are from confined areas where intensive textile dyeing takes place with a total use of dyes amounting to at least 3,500 tonnes p.a., in comparison to the total Danish input of 2,400 tonnes. For the pigments no monitoring studies have been found. Hence, it is not possible to validate these estimates further.

Even though, the PECs are uncertain, it is concluded that there is a release of azo colorants to the environmental compartments, especially to water and soil. The environmental exposure of water may take place as a result of outlet of colorants to waste water during production, processing and end-user consumption. There is a potential indirect exposure of agricultural soils through the application of sludge. Annually, approximately 1,300 tonnes of azo colorants are deposited in landfills and there is a potential release to soil and groundwater from landfills, but the fate of products containing azo colorants, deposited in landfills, is uncertain. It is concluded that predicted environmental concentrations may be established, which may indicate the environmental load, but validation to Danish conditions is not possible due to the lack of monitoring data in Denmark.

In addition, it is concluded that there may be accumulated substantial amounts of colorants in the environment, even though the emissions have been regulated for some years, due to the high accumulation potential of the colorants.

Generally, the availability of published data on the ecotoxicity of azo colorants is very sparse. Therefore, it was only possible to obtain data for a few of the azo colorants used in Denmark. However, short term studies indicate that some of the azo colorants in use are acute toxic (acid, basic and solvent dyes) to aquatic organisms and that others are toxic or potentially toxic (remaining dyes). Only reactive dyes are not considered to be toxic to aquatic organisms. In general, the pigments do not give rise to immediate concern about aquatic toxicity. However, it is indicated that some of them may be potentially toxic. The metabolites are potentially toxic to aquatic organisms, as well.

It is concluded that various azo colorants, representing all the chemical groups consumed in Denmark, may be potentially toxic to aquatic organisms. The metabolites are potentially toxic to aquatic organisms too. However, the limited data availability on ecotoxicity makes it difficult to draw definite conclusions.

The predicted no effect concentration (PNEC) for azo colorants used in Denmark in the aquatic compartment is low:

	Dyes: 0.7 : g/l.
	Pigments: 18 : g/l.

The survey indicates that there is a need of further information, e.g. QSAR or testing, to assess the environmental risk of azo dyes in the STP sludge and the aquatic compartment, except for sediments indicated by PEC/PNEC ratios >> 1, whereas releases associated with sludge applied to soil not seem to present any immediate concern, indicated by PEC/PNEC < 1. As it was impossible to predict the concentration of dyes in landfill soils, the environmental risk for this compartment cannot be established at present.

With regards to azo pigments, the survey indicates that there is a need of additional information or testing in relation to the manufacture of pigments, indicated by PEC/PNEC ratios >> 1, whereas the exposures related to processing and use do not seem to present any immediate concern, indicated by PEC/PNEC ratios < 1.

It is concluded that processing and end-use of dyes as well as the manufacturing of pigments may pose an environmental risk for the microorga- nisms in the sewage treatment plant and for the aquatic compartment, except for sediments. However, this risk assessment is strictly preliminary, because of:

	the aforementioned limitations with regards to estimation of PEC.
	the lack of monitoring data of environmental levels (aquatic and terrestrial) of azo colorants in Denmark.
	the limited knowledge of consumption and use of individual azo colorants - quantities and specific compounds.
	the limited knowledge of the ecotoxicity of the specific compounds.
	the lack of long term low level exposure studies.

Thus, carrying out a "true" risk assessment requires further investigation of the abovementioned parameters, in order to establish a more profound basis for the assessment.

Recommended areas for future investigations

Based on the findings and conclusions of the survey, especially with regard to the assessment of risk in relation to human health and environment, the following focus areas are recommended for future investigation.

The proposed actions are prioritised on the basis of a professional evaluation, taking the potential financial costs into account.

1. It is recommended to elaborate further on the results of the mass balance in order to qualify the balance with regards to specific consumption and use, for:

	Azo colorants consumed by industrial end-users, e.g. the iron and steel industry.
	Dyes at group level and individual dyes.
	Dyes in the trades encompassed by the survey.
	Individual pigments.

2) It is recommended to carry out further investigations on the distribution of dyes and pigments among the environmental disposal routes, i.e. waste water, landfill, incineration and recycling.

For priority 1 and 2, it is suggested that additional information/knowledge is obtained by interviews and questionnaires directed to experts, e.g. from the industry, in a two step approach. The first step may be collection of information of the most representative colorants of the different trades. The second step may, based on the findings of step 1, be collection of information about specific colorants.

3) It is recommended to investigate the general market trends for development and use of organic colorants.

As a feasible approach, it is suggested to conduct interviews with foreign and domestic experts.

4) It is recommended to carry out investigations on the possible content of azo dyes and the associated aromatic amines in imported textile and leather products.

Investigation of the imported goods may be carried out by random sampling and analysis of both large and small batches of textiles from Asia, Eastern Europe, Africa and South America. However, it is very costly to conduct a full monitoring program and, therefore, it is suggested to postpone these investigations, until the results of the more thorough mass balance are established.

1) It is recommended to investigate further on the molecular structure of the colorants used in Denmark and the possible toxicological effects of the other aromatic amines, i.e. besides the 22 well-known. It is known that other aromatic amines may be toxic, like aromatic amines with aryl moieties of anthracene, stilbene, phenanthrene, etc. It may be relevant to know, if azo colorants used in Denmark contain other problematic aromatic amines. In addition, further elaboration on the consumption of disperse dyes and investigation of substitutional options are recommended.

The prerequisite for investigations on molecular structures of colorants used in Denmark is additional knowledge of consumption and use derived from a mass balance study. The possible effects of other aromatic amines, than the 22 well-known, may be clarified through QSAR analysis and grouping.

With regard to investigation of options for substitution of the colorants with the problematic component amines and the disperse dyes, it is suggested, to await the results of a more detailed mass balance of consumption and use and the results of a more thorough analysis of market trends.

2) It is recommended to investigate further on the typical ratios of impurities associated with colorants and products containing colorants, especially associated with imported products.

Information on the typical ratio of impurities associated with colorants may be obtained from experts, e.g. from the industry, and knowledge about impurities associated with products may be obtained by random sampling and analysis of products. The latter may require substantial economic resources, and is suggested to await the results of the former.

3) It is recommended to carry out monitoring studies on occupational environment and to establish an overview of the applied technologies in the manufacturing and processing industries.

Monitoring studies of the occupational environment are quite costly and time-consuming. Therefore, the precondition for carrying these studies is additional knowledge of consumption and use of specific colorants.

Environmental fate and toxicity

1) It is recommended to carry out further investigations of:

	accumulation.
	bioaccumulation.
	biodegradation.
	ecotoxicity (short-term and long-term low level exposure).
	exposure routes.

for the specific azo colorants used in Denmark, with special attention to molecular weight and substitutional pattern.

Additional knowledge of environmental fate and toxicity may be obtained by comparison of more detailed QSAR analysis and the available experimentally assessed data. In this way, it will be possible to address both the most problematic groups and individual colorants.

2) It is recommended to gather information or carry out monitoring studies of the potential releases and environmental concentrations of azo colorants in Denmark, in order to qualify the predictions and in order to establish a more detailed overview of the potential exposures.

With regards to exposure routes and assessment of the environmental risks, the prerequisite is further information of consumption, use and disposal of specific azo colorants in Denmark and to qualify the predicted environmental concentrations. This may be obtained by establishment of a more detailed mass balance and by gathering of information from the municipal authorities on allowed emissions or by actual monitoring studies. However, the latter may not be an economically feasible approach in a short term, and therefore, it is suggested to await the results, that may be obtained by the detailed mass flow analysis.

3) It is recommended to carry out experiments/model studies with regard to the decomposition and potential release of colorants deposited in landfills. Approximately 1,300 tonnes of azo colorants are annually deposited in landfills which may be released to soil and ground water.

Due to the relatively high costs of monitoring studies of landfill soil and leachate, it is suggested to limit the investigation to a thorough literature study of fate of azo colorants in landfills, possibly followed by computerised modelling of the fate of azo colorants incorporated in a product matrix.