UL Solutions: Advancing Water Stewardship in Tanneries

At the ZDHC Europe Conference 2025 in Alicante, Spain, UL Solutions presented a case study that examines the relationship between tanneries’ wastewater test results and chemical product conformance to the ZDHC Manufacturing Restricted Substances List (MRSL). 

This analysis builds on UL’ Solutions' ongoing monitoring of wastewater data in Italy’s major leather manufacturing districts, where conformance remains a critical challenge.
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Wastewater Findings

‍Data shows that only a limited number of tanneries were fully conformant to ZDHC Wastewater Guidelines, with many suppliers either not testing wastewater or not reporting non-conformant results. Where there was data, failures frequently involved contamination by cresols, naphthalene, certain phthalates and chlorophenols.
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Running a Root Cause Analysis

To better understand these issues, UL Solutions conducted a root-cause analysis with one tannery, comparing wastewater samples. The findings identified chlorophenols, 4-chloroaniline, tetrachloroethylene, naphthalene and cresol in both testing cycles. 

Further analysis revealed persistent non-conformant 4-chloroaniline, commonly associated with dyes. Although the tannery used ZDHC MRSL-conformant dyes, trace amounts of 4-chloroaniline, 5-70 parts per million (ppm), were detected, well below the ZDHC MRSL limit (150 ppm), suggesting that even conformant formulations may contribute to low-level contamination.

Verification of over 1,000 formulations’ test results confirmed that only two were non-conformant for 4-chloroaniline. This supports the conclusion that wastewater contamination can originate from trace substances present in conformant chemicals.
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Contaminations‍

UL Solutions' analysis also identified various other contaminations.

• Tetrachloroethylene was traced to incoming water rather than from chemical use. 
• Chlorophenols were detected near reporting limits, which may originate from raw materials, as these can be used as preservatives in leather.  
• Naphthalene was found in 68 out of 217 ZDHC MRSL conformant formulations, at concentrations below ZDHC MRSL thresholds.

UL Solutions’ analysis work findings demonstrate that wastewater non-conformance often may not be due to the use of non-conformant chemicals, but with trace contaminants in incoming water and raw materials playing a significant role. 

Strengthening the link between the ZDHC MRSL and restricted substances list (RSL) requirements is essential. Programmes such as ZDHC Chemical to Zero — Progressive Level (CtZ-P) can further support improved chemical management.
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Wastewater Testing Frequency

UL Solutions' analysis also shows that most tanneries test wastewater only once a year, and many do not test at all. Increasing testing frequency and expanding data collection are essential to identifying trends, addressing root causes and developing industry-wide corrective actions.
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About  UL Solutions‍

UL Solutions, a ZDHC Approved Solution Provider, supports chemical management strategy development for the textile and leather industry and its global supply chains. As an Approved Supplier to Zero Assessor, we are authorised by ZDHC to review supplier submissions in accordance with the Suppliers Roadmap to Zero Framework for the Supplier to Zero programme. 

UL Solutions' services include: 

• ZDHC MRSL Certification
• ZDHC Performance InCheck Report in collaboration with CleanChain
• ZDHC Verified InCheck on-site review
• Wastewater testing and analysis according to ZDHC Wastewater and Sludge Guidelines 
• Official ZDHC trainings

Learn more about UL Solutions’ ZDHC services.

Data taken January 2024-September 2025