Canada Floats Toxic Listing for Ester

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Canada Floats Toxic Listing for Ester
A CNC machining center drilling steel and using metalworking fluid as a coolant. © Daniel

Canada’s health and environment agencies recently recommended regulatory actions for a form of thiophosphate alkyl esters, or TPAE, that is used in metalworking fluids. They include risk management documentation and discussions and addition of the chemical to a toxic substances list.

According to a March 13 Canada Gazette notice, the country’s Minister of the Environment and the Minister of Health conducted a screening assessment of two substances referred to collectively as the thiophosphate alkyl esters, or TPAEs, group.

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The agencies noted that TPAE-1 is the most complex of the two substances, with about 10 major components, including dithiophosphate, thiophosphate and phosphate alkyl ester salts, in addition to a neutral thiophosphate component. With the exception of the neutral component, the departments said all components of these substances are ionized under ambient environmental conditions, and some components – notably aliphatic amine counter-ions – have surfactant properties.

The other substance, TPAE-2, is phosphorothioic acid, 0,0-dibutyl ester, mixed (C8, C16, C18) alkylamine salt.

They identified two industrial uses of TPAEs as having the highest potential for releases to the environment – formulation of lubricants and use in metalworking fluids.

“Environmental concentrations of representative components of TPAE-1 in the aquatic environment associated with releases from these uses, following wastewater treatment, were estimated and compared to predicted no-effect concentrations for aquatic organisms,” the notice reads. “In addition, the concentration of the aliphatic amine components of TPAE-1 in soils following the application of biosolids from wastewater treatment facilities to soil were estimated and compared to a predicted no-effect concentration for soil organisms.

“On the basis of these comparisons, TPAE-1 may pose a risk to aquatic and soil organisms from its use in metalworking fluids,” the agencies concluded.

The agencies noted that, “considering all available lines of evidence presented in this draft screening assessment, there is a risk of harm to the environment from TPAE-1.” They concluded that TPAE-1 meets the criteria under paragraph 64(a) of the Canadian Environmental Protection Act, “as it is entering or may enter the environment in a quantity or concentration or under conditions that have an immediate or long-term harmful effect on the environment or its biological diversity.”

The agencies proposed adding TPAE-1 to Schedule 1 – a list of toxic substances – of the Canadian Environmental Protection Act of 1999.

Conversely, they proposed no action concerning TPAE-2. “TPAE-2 is unlikely to pose a risk to aquatic or soil organisms, based on current usage patterns,” the agencies said in the notice. They also found TPAE-2 to be of low concern for human health at current levels of exposure.

For more information, view pages 10-15 of the Canada Gazette notice online and the Canadian Environmental Protection Act’s Schedule 1 List of Toxic Substances. Written comments will be accepted for up to 60 days from the March 13 publication of the notice, and the agencies released a risk management scope document to initiate discussions with stakeholders on development of risk management options, which may be viewed at Canada’s Chemical Substances website. Publication of the final screening assessment and proposed risk management approach for TPAE-1 is scheduled for March 2022.