China has introduced a biological toxicity requirement for certain textile dyeing and finishing operations under its new wastewater discharge standard, GB 4287-2026. The standard requires covered facilities to demonstrate that fish embryos can survive exposure to treated wastewater, adding a biological assessment alongside conventional chemical limits.

It took effect on September 1, 2026, for new, rebuilt and expanded facilities, while existing facilities must comply from January 1, 2028. The test uses newly fertilised zebrafish eggs exposed to treated wastewater for 48 hours. The wastewater sample is diluted to one-sixth of the test solution, with at least 90% of embryos required to survive under the specified test conditions.

The requirement is intended to assess the combined acute toxicity of treated effluent, rather than individual pollutants such as ammonia or specific metals. It applies to dyeing and finishing operations that discharge directly into rivers, lakes and other water bodies, while mills sending wastewater to shared textile treatment facilities are assessed at the final discharge point.

Bluesign noted that a failed biological test indicates an acute toxic effect under the test conditions but does not by itself identify the cause, which may include residual production chemicals, substances formed during processing or treatment-system issues. Bluesign is separately proposing broader annual biological testing for textile and wet-processing manufacturers, including denim facilities, with fish embryo testing as the preferred method.