Hair dye on photographic film

© Luke Evans

Down the drain

What do we know about the environmental impact of hair dye chemicals?

In the 1990s, environmental researchers first started collecting evidence showing that even at negligible concentrations, the pharmaceutical and personal care products we use daily interfere with the ecosystem.

Today, an increasing number of micropollutants are being identified in rivers around the world. The list of substances regularly detected in waterways includes anti-inflammatories, antibiotics, antidepressants, plasticisers and surfactants. And each year a research scientist or concerned citizen points out an emerging contaminate that has yet to be considered: the most recent examples include artificial sweeteners and fuel additives.

It is a daunting task to keep track of the vast amount of chemicals we use and dispose of into the environment. But in the past 20 years, most nations have incorporated micropollutant monitoring in their environmental assessments. In the USA, a previously unconsidered potential contaminant might gain attention through the U.S. Geological Survey (USGS), an organisation of scientists and technicians in hundreds of locations throughout the country that evaluate its natural resources.

“We are looking at rivers. We’re looking at wastewater – treated and untreated. We are looking at brackish water in wetlands. We are looking at ground water. We are looking at potable and nonpotable. We are looking at produced waters that come up from energy production,” says Alex Demas, public affairs specialist for the USGS.

The USGS has compiled a list of more than 2,500 constituents identified in North American waters. The list is so long because it includes compounds that are naturally occurring, like methane, and compounds that appear in minuscule quantities of little concern. The USGS ranks the constituents into three tiers to prioritise the chemicals that need focused monitoring. Tier 1 compounds require the most attention because they exist in higher quantities and their chemistry causes harm to aquatic life.

The USGS constituent list contains a group of chemicals that could be present in waterways as a result of hair dye disposal. The compounds are ranked Tier 1 owing to their regular occurrence during monitoring; one compound that could be a metabolite of hair colour was found at 79 per cent of urban sites the USGS monitored.

The uncertainty here results from the fact that there are no available data on how hair dyes break down after they enter the environment. How are they affected by the disinfection process at sewage and drinking water plants? How are they metabolised by algae and other aquatic life? What by-products do they leave behind?

These questions are important because metabolites can often be more toxic than parent compounds. Unfortunately, they are often formed in an effort to produce clean drinking water. Before water comes to the tap, it passes through a treatment facility where oxidisers, such as chlorine, are added to the water to kill pathogens and provide a potable water supply.

Dr Ching-Hua Huang, Professor of Environmental Engineering at Georgia Tech University, specialises in disinfection by-products, especially compounds called nitrosamines. “We found that if you have some secondary amines and you put chlorine for oxidation, you will unintentionally generate nitrosamines in your finish water,” says Dr Huang.

David Lewis, a dye chemist and founder of Green Chemicals, proposes that hair dyes – chemically classified as secondary amines – can form these highly carcinogenic compounds after disposal. Nitrosamines exhibit toxicity even at the lowest concentrations, and they induce cancer at exposures of only a part per trillion. Huang agrees with Lewis that the secondary amines used as hair dyes could form stable nitrosamines.

The USGS prioritises the nitrosamine N-nitrosodiphenylamine as a Tier 1 compound because it has been detected periodically in water and sediment. But there is no way to know whether this compound, or any of the potential derivatives of dye chemicals listed as constituents by the USGS, can be linked to the disposal of excess hair colour until research scientists approach the problem from the front end. Someone must study the fate of these compounds in the environment, starting with their trip down the drain.