Control quantity or toxicity of textile chemicals? A case study of denim jeans in the warp-dyeing phase

Abstract

The extensive use and discharge of chemicals is one of the main factors leading to serious environmental pollution in the textiles and apparel industry. The chemical footprint (ChF) is a toxicity-based chemical management method that is used to quantitatively evaluate the potential toxic effects of chemical pollutants discharged during the production of textiles and apparel products on human health and environmental safety. Compared with the traditional quantity-based method, this method needs to simulate the entire process of chemicals from discharge to impact, involving a series of steps of fate, exposure and effect, which greatly increases the difficulty of modeling. A scientific question is whether it is worth spending so much effort to quantify the toxicity of chemicals. Taking the warp-dyeing phase of denim jeans as an example, this paper calculated the ChFs for both human and ecological toxicities of textile chemicals based on the USEtox model, and compared them with the values of discharge quantities. The results reveal that there is a certain inconsistency between the discharge quantity and toxicity of chemical substances. Relying solely on the amount of chemicals discharged can sometimes lead to misjudgments, emphasizing the importance of controlling the toxicity of chemicals.

Keywords

Textile chemical discharge quantity human toxicity ecotoxicity chemical footprint

The consumption and discharge of chemicals occur in various production processes of textiles and apparel, from the use of pesticides in crop cultivation to the application of detergents in garment finishing.¹ Some chemicals, such as heavy metals, organic dyes and alkalis, may cause toxic impacts on biological health and ecological safety.² As necessities in our daily life, textiles and apparel products are in great demand,³ which inevitably increases the consumption of textile chemicals and the amount of chemical pollutants discharged into the environment. Therefore, chemical management and control in the production processes of textiles and apparel products is very important, and it is essential to establish an effective environmental impact assessment method for textile chemicals.

The dominant method currently applied to the management of textile chemicals is to measure and analyze the discharge quantities of chemical pollutants in wastewater or exhaust gas, and control the types and quantities of chemical materials entering the product production chain. In other words, the larger the discharge quantities, the greater the impact on the environment, and the corresponding management measures are to reduce discharge by removing as many of these pollutants as possible before releasing them into the environment, or controlling the usage of chemical materials that generate them in an alternate or obsolete manner.

Some scholars, however, proposed the concept and method of the chemical footprint (ChF). Different from the traditional quantity-based method mentioned above, the ChF method is designed to evaluate the potential toxic effects of chemical pollutants caused by human activities.⁴ It can simulate and quantify the environmental impact of chemicals to the end of the impact chain, that is, the ultimate harm to the human body and the ecological environment,⁵ thereby revealing the objective nature of environmental problems. Substances with greater toxicity can be identified by this method, and then controlled by neutralizing their toxicity or by tracing the chemical material input. Thus far, it has been applied at the scales of products, organizations and regions.⁶^–8 The product-oriented ChF is normally combined with life cycle assessment (LCA) theory⁹ and focuses on the potential toxicity of chemical substances used and discharged during the product life cycle. Based on the risk assessment approaches, Panko and Hitchcock¹⁰ and Hitchcock and Panko¹¹ proposed the definition of the ChF, that is, the potential risk posed by a product based on its chemical composition, the human and ecological hazard properties of the ingredients and the exposure potential during its life cycle.

Roos and Peters¹² first applied the ChF method in the environmental assessment system of textiles and apparel products and compared the human and ecological toxicities of five Swedish garments¹³ using the USEtox model, which was developed as a scientific consensus tool to characterize the toxic effects of chemicals.¹⁴,¹⁵ Based on the primary data provided by Roos et al.,¹³ Qian et al.¹⁶ and Li et al.¹⁷ then calculated and analyzed the values of ChFs for both human and ecological toxicities of denim products during the wet treatment process in more detail. Despite the increasing attention paid to the toxicity control of textile chemicals, no study has yet been conducted with a special focus on the relationship between the quantity and toxicity of chemical pollutants discharged. An important question is whether it is necessary to regulate textile chemicals by quantifying their toxicity. This issue was discussed in this paper, taking the warp-dyeing phase in the production process of a pair of denim jeans as a case study. The effectiveness of the two methods in chemical control was analyzed and compared, aiming to assist apparel manufacturers and environmental managers in making informed decisions.

Methodology and data

General approach

Combined with the theoretical framework of LCA analysis, this study defined the ChF in the textile industry as the potential toxic effect on the human body (i.e., human toxicity) and ecological environment (i.e., ecotoxicity) caused by the discharge of chemical pollutants during the life cycle of textiles and apparel products. The chemicals mentioned were directly involved in any part of the product’s life cycle, excluding the chemical emissions from energy production and fuel use (e.g., carbon dioxide and particulates). The USEtox model was selected as the quantitative tool to account for the ChF, which modeled the links of the cause–effect chain from initial discharge to final impact through the three successive steps of fate, exposure and effect,⁵ as shown in Figure 1.

Figure 1.

The modeling mechanism of the USEtox model.

The ChFs of chemical pollutants can be obtained by introducing their discharge quantities (M, kg) and performing weighted summation with the characterization factor (CF), which is derived from the product of three matrices, namely the fate factor (FF), exposure factor (XF) and effect factor (EF) by the USEtox model,¹⁸ as shown in the following equations

C F = F F \cdot X F \cdot E F

(1)

ChF = \sum_{j = 1}^{8} \sum_{i = 1}^{n} C F_{i, j} \cdot M_{i, j}

(2)

where CF is divided into human toxicity CF and ecotoxicity CF according to different affected objects. For the former, CF represents the number of disease cases per kg of pollutant discharge (cases·kg⁻¹_emitted), while for the latter, CF refers to the potentially affected fraction of species on a given volume and over a given period per kg pollutant discharge ([PAF]m³·day·kg⁻¹_emitted). Here, FF reflects the durability of chemicals in the environment (day) for both human and ecological toxicities, while XF is the bioavailability of a chemical for the human body (day⁻¹), and the dissolution rate of chemical in freshwater for ecotoxicity (dimensionless). For EF, it represents the changes in disease risk over a lifetime due to the intake of chemicals for human toxicity (cases·kg⁻¹_intake), and the influence on the potentially affected fraction of species due to a large increase of a certain chemical for ecotoxicity ([PAF]m³·kg⁻¹). Here, i is the type of chemical substance, while j represents the environmental compartments, which include industrial indoor air, household indoor air, rural air, urban air, sea water, freshwater, natural soil and agricultural soil.

System boundary

To carry out the environmental impact assessment of chemicals used and discharged during the life cycle of textiles and apparel products, the first step is to determine the system boundaries, which include time and space boundaries based on LCA theory.¹⁹ The time boundary refers to the time span between the beginning and end of the life cycle of textiles and apparel products, and the space boundary refers to the inputs and outputs of various chemicals involved in the time boundary of these products.

The industrial production phase of denim jeans discussed here involves a series of processes, including fiber production, yarn spinning, wet treatment, weaving, sewing and finishing, as presented in Figure 2. In particular, the warp of denim fabric is cotton yarn, which is dyed into denim blue yarn by using dyeing machines. The weft yarn is a mixture of cotton fiber and elastic fiber, which needs to be bleached; it is then woven into the denim fabric together with the warp yarn. The jeans are finally finished by cutting, sewing and other processes. The input chemicals here are also known as chemical materials, and the output chemicals are treated as pollutants, which are usually released into the environment in the form of waste gas, waste water or solid waste.

Figure 2.

System boundary of jeans production based on life cycle assessment.

Data collection

This study took the warp-dyeing phase in the wet treatment process of jeans as an example to demonstrate the ChF calculation and compare the quantity and toxicity of chemical pollutants. The functional unit for accounting was set as 1 kg of yarn. The discharge data of chemical pollutants discussed were derived from the study of Roos et al.,¹³ in which reasonable assumptions were made (see Table S1 in the Supplementary material for more details). In the course of obtaining the CFs of various chemical pollutants with the USEtox model, the environmental compartments were set as urban air and freshwater, the environmental parameter was set as Europe and the default values in the model were selected for other parameters. Note that although the USEtox model provides a large number of CFs, the CFs for some chemical pollutants are lacking. To minimize the evaluation error caused by the absence of CFs for the toxic effect of jeans, we applied the USEtox COSMEDE database²⁰ and other references¹²,²¹ as secondary data. The detailed information is shown in Table S2 (see Supplementary material).

Results and discussion

The ChFs for both human and ecological toxicities of chemical pollutants discharged during the warp-dyeing phase of denim jeans were calculated based on Equation (2), and the quantity and toxicity values were then sequenced and compared, as presented in Tables 1 and 2. It should be noted that despite great efforts to collect as much as possible the CF of each pollutant involved, some CFs for human toxicity are still not available, resulting in incomplete results of the corresponding ChFs for human toxicity. For better comparation, only the existing results are analyzed in this paper.

Table 1.

The ranking results for human toxicity

Chemical pollutant	Quantity			Human toxicity
Chemical pollutant	M (kg)	Ranking	Contribution rate	ChF (cases)	Ranking	Contribution rate
Dimethyl siloxane, reaction product with silica	8.91 × 10^–4	1	76.82%	1.29 × 10^–10	1	99.39%
Sodium hydroxide	2.00 × 10^–4	2	17.24%	4.10 × 10^–20	6	0.00%
Oxirane, methyl-, polymer with oxirane, decyl ether	4.50 × 10^–5	3	3.88%	2.36 × 10^–21	8	0.00%
Polyacrylic acid, sodium salt	1.89 × 10^–5	4	1.63%	1.30 × 10^–19	5	0.00%
Hydrogen peroxide	2.75 × 10^–6	5	0.24%	6.66 × 10^–21	7	0.00%
Ethylene oxide	1.00 × 10^–6	6	0.09%	7.43 × 10^–13	2	0.57%
Sodium mono(2-ethylhexyl)estersulfate	1.00 × 10^–6	7	0.09%	1.80 × 10^–22	9	0.00%
Formaldehyde	9.90 × 10^–8	8	0.01%	1.17 × 10^–14	4	0.01%
Magnesium chloride	5.00 × 10^–8	9	0.00%	3.74 × 10^–14	3	0.03%

M: discharge quantity of chemical pollutant; ChF: chemical footprint of chemical pollutant.

Table 2.

The ranking results for ecotoxicity

Chemical pollutant	Quantity			Ecotoxicity
Chemical pollutant	M (kg)	Ranking	Contribution rate	ChF ([PAF]m³·day)	Ranking	Contribution rate
Hydrogen peroxide	5.50 × 10^–3	1	35.55%	1.19	3	17.09%
Indigo	3.98 × 10^–3	2	25.71%	5.61 × 10^–1	4	8.03%
Sodium sulfate	1.50 × 10^–3	3	9.69%	1.01 × 10^–2	11	0.15%
Thiosulfate	1.35 × 10^–3	4	8.73%	1.80 × 10^–2	9	0.26%
Sodium carbonate	1.10 × 10^–3	5	7.11%	3.81 × 10^–2	7	0.55%
Dimethyl siloxane, reaction product with silica	8.91 × 10^–4	6	5.76%	4.88 × 10^–3	12	0.07%
Sulfuric acid	7.50 × 10^–4	7	4.85%	1.00 × 10^–1	5	1.44%
Sodium hydroxide	2.00 × 10^–4	8	1.29%	3.94 × 10^–11	20	0.00%
Nonylphenol ethoxylate	5.45 × 10^–5	9	0.35%	1.63 × 10^–2	10	0.23%
Oxirane, methyl-, polymer with oxirane, decyl ether	4.50 × 10^–5	10	0.29%	1.58 × 10^–11	21	0.00%
Polyacrylic acid, sodium salt	1.89 × 10^–5	11	0.12%	1.33 × 10^–9	19	0.00%
Alcohols, c12-14, ethoxylated	1.80 × 10^–5	12	0.12%	2.95 × 10^–2	8	0.42%
2-methyl-4-isothiazolin-3-one	1.78 × 10^–5	13	0.12%	3.70	1	53.02%
5-chloro-2-methyl-4-isothiazolin-3-one	1.78 × 10^–5	14	0.12%	1.26	2	18.03%
Sodium lauryl sulfate	1.78 × 10^–5	15	0.12%	4.48 × 10^–2	6	0.64%
Isooctyl alcohol	9.00 × 10^–6	16	0.06%	3.10 × 10^–3	13	0.04%
Ethylene oxide	1.00 × 10^–6	17	0.01%	7.36 × 10^–7	18	0.00%
Sodium mono(2-ethylhexyl)estersulfate	1.00 × 10^–6	18	0.01%	1.91 × 10^–12	22	0.00%
Phosphonic acid	9.00 × 10^–7	19	0.01%	4.67 × 10^–4	15	0.01%
Magnesium chloride	5.50 × 10^–7	20	0.00%	4.56 × 10^–6	17	0.00%
Formaldehyde	9.90 × 10^–8	21	0.00%	3.39 × 10^–5	16	0.00%
Nonylphenol	4.50 × 10^–8	22	0.00%	1.37 × 10^–3	14	0.02%

M: discharge quantity of chemical pollutant; ChF: chemical footprint of chemical pollutant.

ChF for human toxicity

According to Table 1, inconsistency occurs between the discharge quantities and the ChFs for human toxicity. Some chemical pollutants with large discharge quantities have small ChFs, for example, sodium hydroxide, while some pollutants with small discharge quantities have high toxic effects on the human body, for example, ethylene oxide. Tracing the discharge source of sodium hydroxide, it mainly comes from the alkali used in the yarn dyeing process. Alkali not only plays a role in removing impurities in the fiber, but also serves to mercerize the cotton fiber for better dyeing affinity, luster and fiber strength.²² It is an indispensable chemical additive, making it in great demand, accompanied by an increase in the discharge of sodium hydroxide. Ethylene oxide is derived from the detergent/wetting agent, which has the functions of wetting, penetrating and cleaning, but its content in the input materials is very low, only 0.1%, resulting in less emissions. Considering the quantity-based approach, managers will tend to pay more attention to the management of sodium hydroxide. However, from the ChF results, ethylene oxide is significantly larger than sodium hydroxide, which means that the former poses greater harm and higher risk to the human body. This is because ethylene oxide is a flammable and explosive gaseous substance at room temperature. As an ocular, respiratory and dermal irritant and a sensitizing agent, ethylene oxide causes respiratory and neurological disorder through long-term or high-dose exposure.²³ Although undiluted sodium hydroxide is highly irritating and corrosive, its concentration as a pollutant discharged into the environment is too small to cause toxicity to the human body, and it is unlikely to cause delayed or long-term effects.²⁴

In addition, it can be found that dimethyl siloxane, a reaction product with silica ranked first in both discharge quantity and human toxicity, with contribution rates of 76.82% and 99.39%, respectively, occupies a dominant position in the chemical pollutants discussed. Its discharge source is the antifoaming agent, applied to eliminate the problems of uneven dyeing and color stains caused by foam. It works essentially by displacing the foam stabilizer from the bubble wall, and thus mechanically destroying the foam by diluting it to the point of rupture.^25,26 In this case, the consumption of antifoaming agent is 0.02 kg, of which 5% is dimethyl siloxane, reaction product with silicon, making the discharge of this pollutant also large. This is one of the reasons for its high human toxicity. On the other hand, according to experimental data, multiple exposure of humans to this compound can cause skin irritation. Due to the long degradation period, its environmental load can last for a long time, making the unit toxicity relatively high.¹⁶

ChF for ecotoxicity

The relationship between the discharge quantities and ChFs for ecotoxicity is similar to that of human toxicity, as shown in Table 2. The small discharge of chemical pollutants does not mean that the toxic effect on the environment is also small. For example, the discharge quantities of two isothiazolinone compounds, that is, 2-methyl-4-isothiazolin-3-one and 5-chloro-2-methyl-4-isothiazolin-3-one, are only 13th and 14th out of the 22 substances discussed. Both of them are derived from the antifoaming agent with a content of only 0.1%. Their ChFs for ecotoxicity, however, rank first and second respectively, with values of 3.70 and 1.26 [PAF]m³·day. This is because the ecotoxicity per unit of both compounds is far greater than that of other compounds. Toxicological studies have shown that isothiazolinone compounds have strong effects on aquatic organisms, such as algae and fish. Prolonged exposure to low concentrations of isothiazolinone compounds may have damaging results on the developing nervous systems of some animals.²⁷ Obviously, focusing only on the quantities of pollutants discharged will ignore the huge potential harm they cause to the ecological environment.

For hydrogen peroxide and indigo, the two pollutants with the largest emissions at 5.50 × 10⁻³ and 3.98 × 10⁻³ kg, their ChFs are inferior to those of 2-methyl-4-isothiazolin-3-one and 5-chloro-2-methyl-4-isothiazolin-3-one, ranking third and fourth, respectively. For them, large discharge quantities are one of the main reasons for their large ChFs. The former is emitted from two chemical materials, that is, bleach and the oxidizing agent, which are used to remove natural pigments from fibers and to make vat dyes chromogenic, respectively. Due to the poor chemical stability, hydrogen peroxide will decompose rapidly in the case of high temperature or heavy metal ions, resulting in high emissions during the production process. Furthermore, the dissociation of hydrogen peroxide is an intense exothermic reaction. If ingested, this chemical may cause various levels of discomfort in the lungs and skin, while the severity of poisoning depends on the concentration of the solution.²⁸ The latter is the most commonly used dyestuff in the warp-dyeing phase of blue denim jeans with a large amount of input.²⁹ Its toxicity mainly manifests in the irritation or corrosion to the skin and eyes of living things.

Conclusions

Considering the importance and necessity of chemical control in the textile industry, this paper compared and discussed two chemical management methods, that is, the quantity-based and toxicity-based methods. The case study of the warp-dyeing phase of denim jeans shows that inconsistency sometimes occurs between the discharge quantity and toxicity of chemical pollutants, reflecting the importance of paying attention to the toxicities of chemical pollutants. Although discharge quantity is one of the key factors affecting the toxic effects of chemicals, quantity-based management is prone to misjudgment. In this case, the discharge quantity of sodium hydroxide is large, but its ChF for human toxicity is relatively small, which means that this compound represents little potential harm to the human body. Given the limited management costs, it may be more effective to give priority to controlling other pollutants with large ChFs, such as ethylene oxide.

The toxicity-based method should be considered in chemical management and control, which enables us to quantify the potential toxic effects of chemical pollution in industrial processes. Through the comparison of ChF values, chemicals with larger toxicity can be identified efficiently, providing an important reference for reducing or avoiding the use and discharge of toxic and hazardous textile chemicals. However, it should be pointed out that limited by the availability of primary data, only the warp-dyeing phase in the life cycle of denim jeans was considered and discussed in this paper, and the conclusions drawn may increase the possibility of environmental burden shifting. In addition, the characterization factors for human toxicity of some compounds are still missing, leading to certain uncertainties in the existing results. To apply the ChF method to actual scenarios in the future, the model needs to be optimized to improve the accuracy and reliability of accounting results.

Footnotes

Declaration of conflicting interests

The authors declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding

The authors disclosed receipt of the following financial support for the research, authorship and/or publication of this article: This work was supported by the Key Project of the Zhejiang Provincial Natural Science Foundation of China (LY21G030004), the Zhejiang Ecological Civilization Institute of the Zhejiang Provincial Key Research Base of Philosophy and Social Sciences (20JDZD076), the Key Projects of the National Social Science Fund (19AZD004) and the K. C. Wong Magna Fund of Ningbo University.

ORCID iD

Yan Luo

References

European Commission. Integrated pollution prevention and control (IPPC) reference document on best available techniques for the textiles industry. Seville: European IPPC Bureau, 2003.

Riaz

Dilshad

Muhammad

, et al. Eco-friendly route for dyeing of cotton fabric using three organic mordants in reactive dyes. Ind Textila 2019; 70: 25–29.

Clarke-Sather

Cobb

Onshoring fashion: worker sustainability impacts of global and local apparel production. J Clean Prod 2019; 208: 1206–1218.

Bjørn

Diamond

Birkved

, et al. Chemical footprint method for improved communication of freshwater ecotoxicity impacts in the context of ecological limits. Environ Sci Technol 2014; 48: 11326–13253.

Rosenbaum

Bachmann

Gold

, et al. USEtox – the UNEP-SETAC toxicity model: recommended characterisation factors for human toxicity and freshwater ecotoxicity in life cycle impact assessment. Int J Life Cycle Ass 2008; 13: 532–546.

Konkel

Chemical footprinting: identifying hidden liabilities in manufacturing consumer products. Environ Health Persp 2015; 123: 130–133.

Sörme

Palm

Finnveden

Using E-PRTR data on point source emissions to air and water—first steps towards a national chemical footprint. Environ Impact Asses 2016; 56: 102–112.

Berthoud

Maupu

Huet

, et al. Assessing freshwater ecotoxicity of agricultural products in life cycle assessment (LCA): a case study of wheat using French agricultural practices databases and USEtox model. Int J Life Cycle Ass 2011; 16: 841–847.

Consoli

Allen

Boustead

, et al. Guidelines for life-cycle assessment: a "code of practise". Pensacola, FL: SETAC, 1993.

10.

Panko

Hitchcock

Chemical footprint: ensuring product sustainability. EM Mag 2011; 12: 12–15.

11.

Hitchcock

Panko

Incorporating chemical footprint reporting into social responsibility reporting. Integr Environ Asses 2012; 8: 386–388.

12.

Roos

Peters

GM.

Three methods for strategic product toxicity assessment–the case of the cotton T-shirt. Int J Life Cycle Ass 2015; 20: 903–912.

13.

Roos

Sandin

Zamani

, et al. Environmental assessment of Swedish fashion consumption. Five garments – sustainable futures . Stockholm: Mistra Future Fashion, 2015.

14.

Hauschild

Huijbregts

Jolliet

, et al. Building a model based on scientific consensus for life cycle impact assessment of chemicals: the search for harmony and parsimony. Environ Sci Technol 2008; 42: 7032–7037.

15.

Hauschild

Jolliet

Huijbregts

MJ.

A bright future for addressing chemical emissions in life cycle assessment. Int J Life Cycle Ass 2011; 16: 697–700.

16.

Qian

Li Y Wang

LL.

Calculation and assessment of chemical footprint of denim fabric. Dye Finis 2018; 44: 52–55.

17.

Luo

Qing

Chemical footprint of textile and apparel products: an assessment of human and ecological toxicities based on USEtox model. J Text I 2020; 111: 960–971.

18.

Huijbregts

Margni

Hauschild

, et al. Usetox® 2.0 user manual (version 2). Lyngby: USEtox® International Center, 2017.

19.

Wang

Ding

, et al. The introduction of water footprint methodology into the textile industry. Ind Textila 2014; 65: 33–36.

20.

Ademe. USEtox COSMEDE, http://efwithusetox.tools4env.com/ (accessed 28 November 2019).

21.

Roos

Holmquist

Jönsson

, et al. USEtox characterisation factors for textile chemicals based on a transparent data source selection strategy. Int J Life Cycle Ass 2017; 23: 890–903.

22.

Varol

Uzal

Dilek

, et al. Recovery of caustic from mercerizing wastewaters of a denim textile mill. Desalin Water Treat 2015; 53: 3418–3426.

23.

Agency for Toxic Substances and Disease Registry (ATSDR) website. Medical management guidelines for ethylene oxide. U.S. Department of Health and Human Services, Public Health Service, GA, https://www.atsdr.cdc.gov/MMG/MMG.asp?id=730&tid=133 (accessed 20 December 2019).

24.

ATSDR. Medical management guidelines for sodium hydroxide (NaOH). U.S. Department of Health and Human Services, Public Health Service, Atlanta, GA, www.atsdr.cdc.gov/MMG/MMG.asp?id=246&tid=45 (accessed 8 December 2020).

25.

Sawicki

GC.

High-performance antifoams for the textile dyeing industry. FL, Boca Raton: CRC Press. 2017.

26.

Environmental Protection Agency (EPA). Safer choice criteria for defoamers. US EPA, Office of Pollution Prevention & Toxics, Washington, DC, https://www.epa.gov/saferchoice/safer-choice-criteria-defoamers (accessed 8 December 2020).

27.

, et al . Acute toxicity of isothiazolinone biocides to pelophylax nigromaculatus embryos and tadpoles. Asian J Ecotoxicol 2014; 9: 1097–1103.

28.

Watt

Proudfoot

Vale

JA.

Hydrogen peroxide poisoning. Toxicol Rev 2004; 23: 51–57.

29.

Blackburn

Bechtold

John

The development of indigo reduction methods and pre-reduced indigo products. Color Technol 2010; 125: 193–207.