Toxicity of azo dyes to benthic invertebrates

Azo dyes are synthetic compounds used as industrial colorants, and some are predicted to be inherently toxic, bioaccumulative, and/or persistent based upon their chemical composition. This study addressed data gaps in current research which included the need to evaluate the toxicity of hydrophobic azo dyes to benthic invertebrates. The toxicity of a solvent dye, Sudan Red G (SRG), and two disperse dyes, Disperse Yellow 7 (DY7) and Disperse Orange 13 (DO13), to Hexagenia spp. and Tubifex tubifex was assessed in spiked-sediment exposures. The dye compounds appeared to degrade readily in the equilibrium and exposure periods, suggesting a limited persistence of the parent compounds in the environment under test conditions.Although azo dye degradation products could not be reliably quantified, one was detected in DY7 sediment samples that elicited toxic effects to Hexagenia and Tubifex, providing evidence that DY7 degrades. Hexagenia survival and growth endpoints responded with similar sensitivity to the dyes, but DY7 was the most toxic, with a 21-day IC25 (concentration associated with 25% inhibition) for growth of 9.6 μg/g. Comparatively, Tubifex reproduction was the most sensitive endpoint for all dyes with 28-day IC25s for young production ranging from 1.3 to 11.8 μg/g. At sublethal concentrations, toxic effects to Tubifex differed between dyes: the solvent dye exerted an effect primarily on gametogenesis (cocoon production), while disperse dyes, most notably DY7, caused effects on embryogenesis(development of worm inside the cocoon). This study indicated that there could be potential hazard to oligochaetes based on the observed effect concentrations, but given the lack of environmental measurements, the risk of these compounds is unknown. Further research is required to determine if degradation products were formed in all dye samples and whether toxicity was caused by the parent molecules, which have limited persistence under test conditions, or by their degradation products. To avoid underestimating toxicity, this study stresses the need to use an infaunal deposit feeder such as the oligochaete Tubifex in sediment toxicity assessments where highly hydrophobic compounds are present.

Supplemental Information

The Chemicals Management Plan (CMP) is a Government of Canada initiative aimed at reducing the risks posed by chemicals to Canadians and their environment. A key element of the Chemicals Management Plan is the monitoring and surveillance of levels of harmful chemicals in Canadians and their environment. Monitoring and surveillance are essential to identify and track exposure to hazards in the environment and associated health implications. Monitoring and surveillance programs provide the basis for making sound and effective public health and environmental health policies and interventions, as well as measuring the efficacy of control measures.

In support of the Chemicals Management Plan, monitoring and surveillance initiatives were established to support Health Canada and Environment and Climate Change Canada scientists, in collaboration with external partners and researchers, to advance our knowledge. This initiative has allowed the Government of Canada to increase its commitment to a number of existing monitoring initiatives, as well as to support new efforts.

For more information on the Chemicals Management Plan, please visit https://www.canada.ca/en/health-canada/services/chemical-substances/chemicals-management-plan.html