Survey of azo-colorants in Denmark

Toxicity and Fate of Azo Pigments

Physico-chemical properties

It was possible to obtain data for 14 out of the 51 pigments encompassed in the present survey (ECDIN; IUCLID; HSDB). The molecular weight of the pigments used in Denmark lies within the range of 293 to 818,51 g/mol, and the average value is 484 g/mol. Generally, the red and orange pigments have lower molecular weights than the yellow pigments.

Pigments have many physico-chemical properties in common with the disperse, solvent and mordant dyes with respect to molecular size and hydrophobity. They have extremely low solubility in water and in the application substrate, but unlike the disperse, solvent and mordant dyes, the pigments also, generally, exhibit a low solubility in organic solvents. For this reason they remain essentially in the solid state during the processing and when they are applied to the substrate (Clarke & Anliker, 1980).

However, some azo pigments are sufficiently soluble under analytical test conditions to yield detectable amounts of the restricted aromatic amines (i.e. greater than 30 mg/kg consumer goods). These azo pigments are included in the German restriction, and amongst them are e.g. Pigment Red 22*, Pigment Red 38 and Pigment Red 8* (ETAD et al., 1995).

Due to the low solubility of azo pigments, hydrolysis may not be an important feature of these pigments. Photolysis, on the other hand, may in principle be possible. Absorption maximum lies within the range of visible and UV-light, but its stability indicates that it will be a slow process.

Diarylide pigments are susceptible to thermal breakdowns at temperatures above 200 ⁰C (ETAD et al., 1995).

The molar weights, melting points and solubility in n-octanol were experimentally measured, and the partition coefficients and solubility in water were estimated for 2 mono and 3 diazo pigments by Anliker and Moser (1987). In addition, data from IUCLID were obtained for 3 azo pigments. The results are given in Table 6.1 below:

n.s. = not soluble.

Data on vapour pressure are not available for most of the pigments. They are, however, large, complex molecules, which can be expected to have lower vapour pressures than disperse dyes, i.e. lower than 10^-13 to 10^-11 mmHg (Baughman & Perenich, 1988b).

Toxicity

Due to the experience with azo dyes, the toxicity of azo pigments has been extensively investigated.

Acute toxicity of azo pigments, as defined by the EU criteria for classification, is very low. In acute toxicity tests, the azo pigments show practically no acute toxicity (NPIRI, 1983).

Highly water insoluble lipophilic azo pigments have shown to be poorly absorbed in the gastrointestinal tract. Consequently, they are not discharged via urine but via unchanged faeces of laboratory animals (Herbst & Hunger, 1993).

Information about the acute oral toxicity including skin and eye irritation, is in the form of material safety data sheets available for many commercial important azo pigments. A great majority of the pigments is non- irritating if tested on skin and mucous membranes.

Sensitisation

Despite a very broad application field, only very few azo pigments, e.g. Pigment Red 3*, 5* and 7 and Pigment Yellow 1* and 3, are known to cause occupational contact dermatitis in heavily exposed painters. However, only a few pigments have been tested in the clinic or in animal tests. (Ullmann, ^5th Edition; Foussereau et al., 1982).

Toxicokinetic

Reduction and cleavage of azo linkage in vivo, resulting in recognised carcinogens, were the main concern regarding azo dyes. The apparent generality of this metabolic pathway has prompted concern about the potential hazards associated with exposure to azo pigments.

An earlier work by Akiyama in the seventies seemed to show that rabbits are able to metabolise Pigment Yellow 13* to the component aromatic amine 3,3´-dichlorobenzidine. An extensive research on several animal species, inclusive primates, has strongly contradicted these results.

Of particular interest are azo pigments, which theoretically may release 3,3´-dichlorobenzidine. Pigment Yellow 12*, a diazo pigment based on 3,3´-dichlorobenzidine, seems to be a model compound, as it is most widely applied for toxicological studies of azo pigments. The oral and dermal absorptions and distribution of Pigment Yellow 12 were investigated in rats. After oral administration, the entire dose was accounted for in faeces. Furthermore, Pigment Yellow 12*, 13* and 17* were rather extensively investigated for hypothetical release of aromatic amines in vivo according to the three exposure routes: oral, dermal and inhalation. In no case any presence of the metabolic cleavage of the azo linkage was shown (Herbst & Hunger, 1993).

Water solubility is a prerequisite for absorption and metabolism in vivo. Azo pigments are not soluble in water and therefore, in practice, not available for metabolic activity. Consequently, directly excreted in the faeces without any absorption or participation in the enterohepatic circulation.

Mutagenicity

A majority of azo dyes requires metabolic reduction and cleavage of the azo linkage to component aromatic amines, to show mutagenicity in vitro test systems. Azo pigments, which are not available for metabolic activity, do not show mutagenic properties in vitro.

In the early eighties, Ames’ test was applied for testing of azo pigments, namely Pigment Yellow 1*, 12* and 74*, Pigment Orange 5* and 13* and Pigment Red 1*, 22*, 23, 48*, 49*, 53 and 75. With the exception of Pigment Orange 5* and Pigment Red 1*, which were found weakly positive, all of the tested pigments were negative (NPIRI, 1983).

In connection with the testing for carcinogenicity, two azo pigments, Pigment Red 3* and 53*, have been extensively tested for mutagenicity. Pigment Red 3* did not induce gene mutation in bacteria or sister chromatid exchange or chromosomal aberrations in cultured mammalian cells (IARC, 1993).

Pigment Red 53* was inactive in all studies for mutagenicity, in which the DNA damage in cultured mammalian cells and in rodents in vivo, the sister chromatid exchange and chromosomal aberrations in cultured mammalian cells and micronucleus test in rats, treated orally, were tested. The test also included assays for gene mutation in bacteria and cultured mammalian cells (IARC, 1993).

Carcinogenicity

Based on the experiences with azo dyes, the probable carcinogenicity of azo pigments has been of main concern. Although epidemiological studies have not revealed any risks, several carcinogenicity studies have been carried out with azo pigments.

Dichlorobenzidine based pigments, e.g. Pigment Yellow 12*, 16* and 83* were investigated in long-term feeding studies in rats and mice. The daily dosage for rats were up to 0.6 g/kg body weight and for mice up to 2 g/kg body weight. No carcinogenic effects were observed. For Pigment Yellow 12*, two subsequent studies were carried out and both with negative results (Herbst & Hunger, 1993).

Pigment Red 3 is one of the most widely used red pigments for colouring of paints, inks, plastics, rubber and textiles. The pigment was tested for carcinogenicity in rats and mice. In those species only limited evidence for carcinogenicity was established. An overall evaluation of the pigment, carried out by IARC, stated that it cannot be classified as to its carcinogenicity to humans (IARC, 1993).

Pigment Red 53:1 is very widely used in cosmetic products and as drugs in some countries. Furthermore it is used in printing inks, coated papers, crayons, rubber etc. In experimental animals the pigment was tested in two studies in rats and one study in mice. In addition, a long-term skin painting study was carried out on mice. Only limited evidence for carcinogenicity was established in rats, but in mice no evidence for carcinogenicity was found. The pigment was inactive in a very broad spectrum of mutagenicity tests. An overall evaluation of the pigment, carried out by IARC, stated that the pigment is not classifiable as to its carcinogenicity to humans (IARC, 1993).

Problems of impurities

Impurities in pigments may be introduced via contaminated raw materials and/or intermediates used in the manufacturing process. Impurities are mainly found in trace amounts and encompass:

	heavy metals
	aromatic amines
	polychlorobiphenyls
	polychlorinated dioxins and/-furans ("dioxins")

Heavy metals may be found as impurities of raw materials and/or intermediates. The following heavy metals have been found in pigments: antimony, arsenic, barium, lead, cadmium, chromium, mercury and selenium. Upper limits for the content of heavy metals in pigments are established within certain areas of application, e.g. toys and paints.

Aromatic amines used for synthesis of pigments may be found in trace amounts. The following aromatic amines have been found in pigments:

4-aminobiphenyl, benzidine, 2-naphthylamine and 2-methyl-4-chloro- aniline. Upper limits for the content of aromatic amines have been defined for certain areas of application, e.g. packaging material for foods.

Polychlorobiphenyls (PCB) and polychlorinated dioxins and furans may, due to various site reactions, be found in trace amounts in azo pigments deriving from chloroaniline or dichloro- or tetrachlorodiaminodiphenyl. Furthermore, pigments, which are manufactured in the presence of solvents like di- or trichlorobenzene may contain traces of PCBs, formed by site reactions too.

Exposure

Exposure to azo pigments may entail exposure to the component aromatic amines due to:

presence of aromatic amines as impurities (their intermediates).

Exposure to aromatic amines is of greatest concern, as many of them are characterised by serious long-term effects.

Exposure to azo pigments may take place through inhalation and accidental ingestion. Absorption of azo pigments through the skin is doubtful, whereas impurities may be absorbed, e.g. aromatic amines.

In Denmark, occupational exposure to azo pigments may take place within manufacturing processes and some other industrial sectors, mainly manufacturing of paints and inks, colouring of plastics and printing. Furthermore, the exposure may take place in several hand-craft sectors, e.g. painting.

Non-occupational exposure to azo pigments may take place within a few areas, e.g. home decorating.

Summary

The acute toxicity of azo pigments is very low.

Only a few pigments have been linked to allergic contact dermatitis, and in all cases in extensively exposed painters. These pigments were among the earliest synthetic organic pigments and are now replaced with pigments of greater fastness to light.

Azo pigments are due to their very low solubility in water, in practise, not available for metabolic activity. Consequently, metabolic cleavage to the component aromatic amines has not been shown.

Azo pigments do not show carcinogenic potential neither in humans nor in experimental animals. However, the presence of aromatic amines as impurities in commercially available azo pigments or during the synthesis (manufacture) of pigments, may depend on the actual exposure and constitute a risk for human health.

There is a small but potential risk of exposure to potentially carcinogenic aromatic amines from azo pigments in Denmark. Occupational exposure may take place within the manufacturing process and in some industrial sectors, mainly manufacturing of paints and inks, colouring of plastics and printing. Furthermore, the exposure may take place in several hand-craft sectors, e.g. painting. Non-occupational exposure may take place within a few areas, e.g. home decorating.

Environmental fate and exposure

Measured data concerning the emissions of azo pigments to the environment in Denmark are not available. This applies both for the production phase and the processing and use phases.

There is a possible release of azo pigments to waste water effluent during the production phase from the one Danish manufacturer of pigments and the processing industries: print, paint, textile and leather. However, compared to the azo dyes, the emissions are lower from these processing industries. The contribution to waste water effluent from the plastic and paper industries is negligible.

It is assumed that there is no significant release of pigments to waste water during the use phase (consumption of end-products). The predominant release from this phase is to landfills.

A potential release route to the atmosphere may be from pigments bound to particular matter in soil/sludge from either landfills or agricultural fields fertilised with sludge or from incineration of waste and emissions from the processing industry. However, this release route may not be very important, due to the physical-chemical properties of the pigments. It is assumed that the atmospheric release route is negligible, i.e. approximately 0.

Agricultural fields fertilised with sludge may give rise to soil and groundwater releases of pigments. Landfills may provide another release route of pigments to these compartments.

The estimated Danish releases are summarised in Table 6.2 below. The preconditions for the estimates are given in chapter 4.

n.a. = negligible amount.

As for the azo dyes, impurities of the pigments as well as decomposition by reductive cleavage may result in transformation of the azo pigments into the degradation products, i.e. metabolites - aromatic amines - of which some are potentially carcinogenic. Estimation of the decomposition of azo pigments in the environment may be derived from knowledge of the azo pigments’ structural and molecular composition and a stoichiometric equation.

The aspect of the metabolites is discussed in connection with the azo dyes in chapter 5, section 5.3 and section 5.4.

Degradation

Hydrolysis is not considered to play any role in the degradation of pigments in the environment, due to their physico-chemical properties as highly hydrophobic substances. This is supported by a study on Pigment Yellow 83* of which hydrolysis was not detected in a 56-day experiment (IUCLID).

Photolysis of pigments is, in principle, possible. Stability of the pigments to visible and UV light are very high, therefore, only slow degradation may take place (Clarke & Anliker, 1980).

Subsequently, abiotic degradation of azo pigments may not be very probable.

The pigments are practically insoluble and therefore considered essentially non-bioavailable (ETAD, 1989).

Biodegradation studies carried out on Pigment Yellow 17* showed that no anaerobic biodegradation occurred (ETAD et al., 1995). The rate limiting step for biodegradation by bacteria may be the uptake over the membrane, according to the findings of Opperhuizen et al. (1985), where it was shown that xenobiotics, with a cross section of more than 9.5 Å, are not able to pass the cellular membrane.

Furthermore, data on biodegradation of two other pigments included in the present survey: Pigment Red 53* and Pigment Yellow 12* indicated that no biodegradation took place in a 2-week study with sludge concentrations of 30 mg/l of the pigment (MITI). The same applies for Pigment Yellow 83* (IUCLID).

According to IUCLID, aerobic degradation by activated sludge may take place. In 15-day studies 40 and 81% of Pigment Yellow 83* and Pigment Yellow 12*, respectively, were degraded. However, it should be noted that the pigments were dispersed in, among other things, ethandiol.

The white-rot fungus Pycnoporus cinnabarinus has been able to decolourise the effluent from a pigment plant, up to 90% in 3 days. The biodegradation was by way of extracellular oxidases (Banat et al., 1996).

Biodegradation of azo pigments may be insignificant at least in relatively short term studies, indicating that they are not biodegradable, neither ready nor inherent. No data were found on long term studies and biodegradation. It is concluded that pigments are likely to persist in the environment.

Intracellular biodegradation of azo pigments which is considered to be the main degradation route of bacteria is not feasible for pigments due to the large molecular size. However, it seems that there is a potential for biodegradation by means of extracellular enzymes and when the pigments are dispersed in reagents.

Distribution

In principle, pigments like disperse and solvent dyes are potentially volatile, but as they are large, complex molecules, they can be expected to have low vapour pressures, i.e. lower than 10^-13 to 10^-11 mmHg. Another reason for volatilisation to be unlikely for the uncharged pigments is that the escaping tendency or fugacity that drive volatilisation is also the driving force for both sorption and bioconcentration (Baughman & Perenich, 1988b).

The pigments are highly hydrophobic and like the non-ionic dyes (e.g. disperse dyes), they adsorb strongly to sediment and soil.

Tests indicate that dyes adsorb 40-80% (Clarke & Anliker, 1980). Due to the physico-chemical properties of pigments (e.g. Log K_ow,), it is assumed that pigments adsorb strongly which indicates an adsorption of at least 80 to 98%. According to the TGD (1996) an adsorption of approximately 92% may be expected.

Furthermore, pigments do not reach open waters to any significant extent due to the extremely low water solubility and molecular weight. The pigments may be found on soil/sediment/sludge fraction due to precipitation. (Clarke & Anliker, 1980).

As for the disperse dyes it may be expected that the sorption of pigments to sediment is dependent of the substitutional pattern of the chemical structure of the pigments, pH, the organic content of waste water as well as salinity. Sorption is favoured by decreasing pH and increased salinities (Weber, 1991; Pagga & Taeger, 1994).

No data were obtained on adsorption of pigments, but it is indicated that this route of removal is most important. It is assumed that pigments adsorb or precipitate 80 to 98% in the aquatic environment.

Bioaccumulation

Products which are almost completely insoluble in water present particular experimental difficulties both in fish accumulation tests and by mea- surement of partition coefficients (Clarke & Anliker, 1980).

Anliker and Moser (1987) studied the limits of bioaccumulation of organic pigments in fish and their relation to the partition coefficient and the solubility in water and octanol for 2 azo pigments: a tetrachloroisoindoli- none type and a phenyl azo-2-hydroxy-naphthoicacid type. They found:

	Estimated solubility in water 10-9 and 10-7 mg/l, respectively.
	Solubility in n-octanol <1 and <0.1 mg/l, respectively.
	Estimated log Kow 10.5 and 10.1, respectively.
	Experimentally assessed log BCF 0.48 and 0.70, respectively.

The high log K_ow would suggest strong bioaccumulation tendencies, but no accumulation was observed in the fish for the pigments tested. The reason for this apparent inconsistency is the very limited fat (lipid) storage potential of these pigments, indicated by their low solubility in n-octanol and their large molecular size. In addition, the findings of Opperhuizen et al. (1985) indicate that a lack of uptake can be expected for extremely hydrophobic chemicals with an effective cross section larger than 9.5 Å (0.95 nm), like the pigments described, because the membrane permeation seems practically impossible.

Studies of bioaccumulation of pigments by Anliker et al. (1981) and Anliker et al. (1988) are in agreement with the above stated results. In the study of 1988 the two pigments examined had cross sectional diameters of 0.97 and 1.68 nm, respectively, and the corresponding log BCFs were 0.48 and 0.70 (MITI standard), respectively.

In addition, the low solubility effects are further enhanced, because the dissolution rates for extremely insoluble hydrophobic solids are usually very low causing that equilibration with water may take months or even years (Anliker et al., 1981).

Only a few experimentally assessed data on log BCF of the pigments encompassed in the present study, were available (Table 6.3).

Table 6.3

Biokoncentrationsfaktorer for nogle azopigmenter anvendt i Danmark.

By the bioaccumulation factor, it is indicated that the immediate concern for bioaccumulation of azo pigment may be very low.

Aquatic compartment

Monitoring data

Only negligible amounts of pigments reach the environment, owing to their extremely low water solubility (10^-6 to 5 mg/l) and their application in mostly non-aqueous systems (Anliker, 1986). The loss of organic pigments to the environment is estimated to be 1% in the production and 1 to 2% during the processing (Clarke & Anliker, 1980).

No monitoring data of azo pigments were obtained in the aquatic compartment.

Estimation of PEC

In the present calculation of PEC _{effluent, stp}, two scenarios will be presented. The estimation of PEC _{effluent, stp} is based on the following assumptions

The production and processing industries do not treat waste water.

Between 80 and 98% (adsorption and precipitation) of the azo pigments are adsorbed and/or precipitated in the sewage treatment plant (STP) (Clarke & Anliker, 1980). This results in a worst case scenario of 80% adsorption and precipitation (20% are released to the effluent) and a best case scenario of 98% adsorption and precipitation (2% are released to the effluent).

Adsorption to sludge and sediment is calculated based on a worst case of 98% adsorption and precipitation and a best case of 80% adsorption and precipitation.

Adsorption is the only removal route of the azo dyes in the STP, i.e. there is no abiotic or biotic degradation.

Furthermore, a standard STP scenario in compliance with TGD (1996), is used. According to this standard, the following values are standard characteristics:

Table 6.4

Standardkarakteristika for et rensningsanlæg.

1 STP: Sewage Treatment Plant.

Ref.: TGD (1996).

The calculation of PEC _{influent, stp} is simplified and based on the equation below:

PEC_{influent, stp} = Release_{waste water} /Waste_{inhab. ´} Capacity_{stp ´} 365

The calculation of PEC _{effluent, stp} is simplified and based on the assumptions mentioned above. In addition the PEC _{effluent, stp} for the processing industry is corrected for the number of sites present in Denmark, e.i. 1 production site, 40 sites for textile colouring and 1 site for leather dyeing and for the use, the number of inhabitants in Denmark (approximately 5 millions) is normalised to the capacity_stp.

PEC _{effluent, stp} = PEC _{influent, stp} ´ (1- adsorption factor)/(number of sites) or inhabitants in Denmark.

PEC _{surface water} = PEC _{effluent, stp ´} dilution factor. According to the TGD (1996), the dilution factor is 10.

In Table 6.5, the estimated PEC_{effluent, stp} and PEC_{surface water} for azo pigments are presented.

Table 6.5

Estimated PEC _{effluent, stp} and PEC_{surface water} for azo pigments.

Estimeret PEC_{udløb, stp} og PEC_{overfladevand} for azopigmenter.

	Release	PEC influent, stp	PEC effluent, stp	PEC effluent, stp	PEC surface water	PEC surface water
	t/year	mg/l	mg/l/site or inhab.	mg/l/site or inhab.	mg/l/site or inhab.	mg/l/site or inhab.
			Worst case	Best case	Worst case	Best case
Pro- duction	180	246	49.3	4.93	4.93	0.49
Pro- cessing
Textile	2	2.7	0.014	0.001	0.001	0.0001
Use
Textile	8	10.9	0.004	0.0004	0.0004	0.00004
Total	190	-	-	-	-	-

The PEC_sediment is calculated from:

PEC_sediment = PEC_{surface water} ´ adsorption factor.

In Table 6.6 the PEC_sediment is presented.

Table 6.6

Estimated PEC_sediment for azo pigments

Estimeret PEC_sediment for azopigmenter.

Scenario	PECsurface water	Adsorption factor	PECsediment
	mg/l		mg/kg
Worst case
Production	4.93	0.98	4.83
Processing
Textile	0.001	0.98	0.00098
Use
Textile	0.0004	0.98	0.00039
Best case
Production	0.49	0.80	0.392
Processing
Textile	0.0001	0.80	0.00008
Use
Textile	0.00004	0.80	0.000032

Concerning the concentration of azo pigments in the sludge, the estimation is based on an annual production of sludge of 170,000 tonnes dry weight in Denmark (Miljøstyrelsen, 1996b). The worst case of adsorbed azo pigments to the sludge is 98%, and the "best case" is 80% of adsorbtion. The calculated concentration in sludge is based on the following equation:

PEC_sludge = (Release ´ Adsorption factor ´ 10⁶/ Sludge rate)/(Number of sites) or inhabitants.

Sludge rate = 170.000 tonnes/year.

Table 6.7

Estimated PEC_sludge for azo pigments.

Estimeret PEC_slam for azopigmenter.

	Release	PECsludge	PECsludge
	t/year	mg/kg/site or inhab.	mg/kg/site or inhab.
		Worst case	Best case
Production	180	1,037	847
Processing
Textile	2	0.29	0.24
Use
Textile	8	0.09	0.08
Total	190	-	-

The estimated PEC_{effluent, stp} and PEC_{surface water} are very high from the production of azo pigments in the range of 4.9 to 49.3 mg/l and 0.49 to 4.93 mg/l, respectively, whereas from the processing and use phases they are much lower in the range of 0.04 to 1 : g/l (PEC_{surface water}).

Due to the lack of monitoring data of environmental concentrations of azo pigments, it is not possible to validate the estimated PECs, but the basic assumption that the manufacturing and processing industries do not carry out waste water treatment prior to outlet (PEC_{influent, stp}) is unlikely, because most of these companies, if not all of them, 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, the companies are obliged to have some degree of waste water treatment prior to the outlet to the municipal STP. This indicates that the estimated PEC_{influent, stp} generally is to high.

Furthermore, the pigments are only sparingly soluble in water and may rather quickly be bound to the particulate matter or sludge if subjected to waste water treatment.

This indicates that the actual PEC_{effluent, stp} and PEC_{surface water} for the production phase are more likely to be in the range of 1 to 9.9 mg/l and 0.1 to 1 mg/l, respectively. The latter is still very high, because there will be a visual colouring of the water above concentrations of 1 mg/l. Recalculating the PEC_{effluent, stp} and PEC_{surface water} for the processing and use phases in the same way, results in concentrations of 0.02 to 4 : g/l and 0.002 to 0.4 : g/l, respectively.

If it is assumed that the PEC_{surface water} is to high, then the PEC_sediment has to be reduced in the same order of magnitude. Resulting in a concentration of 0.1 to 1 mg/kg from production and 0.002 to 0.4 : g/kg from processing. However, as shown in the monitoring studies on dyes, there may be significantly higher concentrations in the sediment compared to the water phase.

If it is assumed that the companies carry out waste water treatment and that 80% of the pigments are removed in this way, 20% may be released to the waste water outlet (worst case). The PEC_{sludge, stp} may be reduced to 212 mg/kg for production and 0.14 mg/kg for processing and use.

Atmosphere

Monitoring data

No monitoring data of azo pigments were obtained in the atmosphere.

Estimation of PEC

It was not attempted to calculate the atmospheric PEC, but it is estimated that the PEC is very low, because volatilisation is highly unlikely for the azo dyes from both moist and dry surfaces. Furthermore, release from the processing industry and from incineration is considered to be very low (approximately equal to 0).

Terrestrial compartment

Monitoring data

No monitoring data of azo pigments were obtained in the terrestrial environment.

The sources of environmental releases of azo pigments in the terrestrial environment are waste disposal in landfills and sludge applied as fertiliser in agriculture.

Estimation of PEC

It is estimated that the total amount of sludge per year in Denmark is 170,000 tonnes dry weight. About 114,000 tonnes (67%) are used in agriculture and 20,000 (12%) are deposited in landfills. The rest is incinerated (21%) (Miljøstyrelsen, 1996b).

It is not known how many hectares of agricultural soil that are fertilised with sludge in Denmark. But according to the TGD (1996), the following characteristics of soil and soil use are accepted:

Table 6.8

Standard environmental characteristics for soil.

Standard miljøkarakteristika for jord.

	Depth of soil	Rate of sludge application
	[m]	[kgdwtxm-2xyear-1]
PEClocalagr. soil	0.20	0.5

Ref.: TGD (1996).

In section 2.3.4 of the TGD (1996), standard environmental characteristics are defined and on this basis it may be calculated that the density of soil is 1.7 tonnes/m³. By application of a depth of soil of 0.2 m in accordance with the TGD (1996), it is estimated that the weight of soil per square meter is equal to 0.34 tonnes.

Subsequently, assuming this, 98% of the azo pigments are adsorbed to the sludge in a worst case scenario and 80% are adsorbed to sludge in a best case scenario. The amount of azo dyes on the agricultural fields can be estimated from the following equation:

PEC_{agri sludge} = (release ´ adsorption factor ´ fraction to agriculture)/ (sludge amount/application rate) ´ soil weight.

Table 6.9

Estimated PEC_{agri sludge} for azo pigments.

Estimeret PEC_{agri slam} for azopigmenter.

	Release	PECagri sludge	PECagri sludge
	t/year	mg/kg	mg/kg
		Worst case	Best case
Production	180	1.53	1.23
Processing
Textile	2	0.02	0.01
Print (de-inking)	50	0.65	0.43
Use
Textile	8	0.08	0.06
Total	190	-	-

The allocation of sludge to landfill disposal amounts to 20,000 tonnes dry weight per year. The contribution of sludge adsorbed azo dyes to the total amount of azo dyes in landfills may be calculated on the basis of the equation shown below:

Sludge amount to landfill = release ´ adsorption factor ´ fraction to land- fill.

In a worst case scenario, the contribution from the one production site may be 20.8 tonnes/year and from processing and use 0.23 tonnes/year. In a best case scenario, the values are 16.9 and 0.19 tonnes/year, respectively. This corresponds to approximately 2 and 0.02% of the total amount of pigments deposited in landfills from the manufacture of pigments and > 0.1% from the processing industries.

Thus, the total release to landfills may be estimated to approximately 1,021 tonnes/year (worst case) 1,017 tonnes/year (best case).

Assuming that 80% of the pigments are removed by the waste water treatment facility at the production and processing sites, the PEC_{agri sludge} from production may be reduced to 0.311 mg/kg soil and from processing to 0.003 mg/kg soil. The contribution from the use and de-inking phases are unchanged 0.07 and 0.65 mg/kg soil, respectively. However, due to the lack of monitoring data, it is not possible to validate the calculated PECs. But the concentration is in the same order of magnitude as the worst case level of 1 mg/kg for dyes, reported by Brown and Anliker (1988).

The fate of products containing pigments released to landfills is uncertain, but there may be a potential release of pigments to soil from this compartment.

Ecotoxicity

Aquatic compartment

The possible inhibitory effects of dyes, including 3 pigments, on aerobic waste water bacteria have been studied by Brown et al. (1981). For Pigment Orange 34, Pigment Red 9* and Pigment Yellow 13*, the IC₅₀ was above 100 mg/l measured as the respiratory rate. The experimental results for Pigment Red 9* indicate that only some of the bacteria appeared to be sensitive to the pigment, but this sensitivity extended over a rather large concentration range. The IC₅₀ found by extrapolation was 350 mg/l.

According to IUCLID, Pigment Red 53* has an IC₅₀ at 24 hours of more than 1,500 mg/l and Pigment Yellow 12* an IC₅₀ of more than 2,000 mg/l.

Based on literature and database studies, it was possible to obtain LC₅₀ data for a few azo pigments on various fish species. The data are listed in Table 6.10 below.

Table 6.10

Effect of azo pigments used in Denmark.

Effekt af azopigmenter anvendt i Danmark.

C.I. name	Fish	Effect	Concentration
	Organism		mg/l
Pigment Orange 13	Cyprinus carpio1	LC50, 48 h	100
Pigment Red 53	Cyprinus carpio1	LC50, 48 h	420
	Brachydanio rerio3	LC50, 48 h	>500
	Oryzias latipes3	LC50, 48 h	>420
	Brachydanio rerio3	LC50, 96 h	>500
Pigments Yellow 12	Cyprinus carpio1	LC50, 48 h	>420
	Leuciscus idus3	LC50, 48 h	>500
	Leuciscus idus3	LC50, 96 h	>100
Pigment Yellow 83	Phoxicus phoxicus1	LC50, 48 h	45
	Oncorhynchus mykiss1	LC50, 48 h	18
	Leuciscus idus1	LC50, 48 h	45
1 Data from MITI. 2 Data from AQUIRE. 3 Data from IUCLID.

Summary

Short term studies indicate that azo pigments do in general not give rise to immediate concern about toxicity, as the toxic effects are exhibited at levels above 100 mg/l. But the effect concentrations for Pigment Yellow 83 indicate that this pigment is potentially toxic (LC₅₀ 10 to 50 mg/l).

The very limited data availability on short term effects of pigments and the lack of long-term studies on effects, makes it difficult to draw general conclusions on the toxicity of azo pigments, but compared to the azo dyes, their toxicity to aquatic organisms is in general lower.

PNEC - aquatic

Applying an assessment factor of 100 on the EC₅₀ from a respiration inhibition test (IUCLID), the following PNEC is derived according to TGD Part II, section 3.4:

PNEC_stp = 15 mg/l

Despite the fact that short term data from each of the three trophic levels (alga, fish, daphnia) were not obtained in the present survey, the assessment factor of 1,000, according to TGD Part II, section 3.3.1, is applied at the lowest LC₅₀. The lowest observed effect is for fish (Table 6.10) , i.e. the LC₅₀ of 18 mg/l for Oncorhynchus mykiss, arriving at a PNEC of :

PNEC_{aquatic organisms} = 18 : g/l.

Atmosphere

No data were obtained on atmospheric exposure.

Terrestrial compartment

No data were obtained on terrestrial exposure.

Risk characterisation

The PEC/PNEC ratios which can be derived with the available data are shown in Table 6.11 and Table 6.12.

Table 6.11

PEC/PNEC ratios for the aquatic and terrestrial compartments from manufacture (production).

PEC/PNEC ratioer for vand- og jordmiljø fra fremstilling (produktion).

Compartment	Site	PEC (mg/l or kg)			PEC/PNEC
		Worst	Best	Worst		Best
STP	STP sludge	1,037	847	69		56
Aquatic	STP effluent	49.3	4.9	2,738		272
	Surface water	4.93	0.49	273		27.2
	Sediment	4.83	0.392	0.32		0.03
Terrestrial	Agr. sludge	1.53	1.23	-		-

Table 6.12

PEC/PNEC ratios for the aquatic and terrestrial compartments from processing and use.

PEC/PNEC ratioer for vand- og jordmiljø fra procesanvendelse og brugsfasen.

Com- partment	Site	Site	PEC (mg/l or kg)		PEC/PNEC
			Worst	Best	Worst	Best
STP	STP sludge	Pro- cessing
		Textile	0.29	0.24	0.019	0.016
		Use
		Textile	0.09	0.08	0.006	0.005
Aquatic	STP effluent	Pro- cessing
		Textile	0.014	0.001	0.8	0.06
		Use
		Textile	0.004	0.0004	0.2	0.02
	Surface water	Pro- cessing
		Textile	0.001	0.0001	0.06	0.006
		Use
		Textile	0.0004	0.00004	0.02	0.002
	Sedi- ment	Pro- cessing
		Textile	0.00098	0.00039	0.0001	0.00003
		Use
		Textile	0.00008	0.000032	0.000005	0.000002
Terrestrial	Agr. sludge	Pro- cessing
		Textile	0.02	0.01	-	-
		Printing (De- inking)	0.65	0.45	-	-
		Use
		Textile	0.08	0.06	-	-

For substances with a PEC/PNEC ratio of < 1, according to TGD, there is no need for further testing and no need for risk reduction measures beyond those which are already being applied, whereas a ratio > 1 indicates a need for further information and/or testing or even a need for limiting risks.

The PEC/PNEC ratios from the production of pigments are well above 1 (Table 6.11), indicating a need for further testing, whereas the ratios for processing and use are well below 1 (Table 6.12), indicating that there is no immediate (acute) risk.

With reference to the assumptions and recalculation of the PECs, it is indicated that the PEC/PNEC ratios presented in Table 6.11and Table 6.12 are to high. Subsequently, the PEC/PNEC ratios for production may be in the range:

PEC/PNECsludge, stp	0.01 to 14	>1
PEC/PNECeffluent, stp	56 to 556	>>1
PEC/PNECsurface water	5.6 to 56	>1
PEC/PNECsediment	0.007 to 0.07	<1

Recalculation of the PEC/PNEC ratios for processing indicates a range well below 1 which indicates that there is no immediate need for further testing.

Summary

Subsequently, the survey indicates that there is a need for further information and testing in order to assess the environmental risk associated with the manufacturing of azo pigments, whereas the releases associated with processing and use not seem to present any immediate concern.

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