Regulators have hit LNG exporter Inpex with a warning after a second toxic mercury incident at its operations off WA’s coast.

The National Offshore Petroleum Safety and Environmental Management Authority on Tuesday directed Inpex to bring in independent experts to review mercury emissions at two facilities about 450km from Broome.

It followed an investigation into Inpex after the company disclosed an accidental discharge of mercury sulphide into the ocean in September.

That came just weeks after an incident where offshore workers were reportedly exposed to the chemical.

Mercury is listed on the World Health Organisation’s top 10 chemicals of major public health concern and is subject to a special international convention on waste management.

NOPSEMA warned Inpex that its actions were “inconsistent” with the controls in place for mercury in its environmental plan.

“Critical systems and processes relied upon in the (plan) to manage hazardous substances and associated emissions and discharges are not being implemented, or are operating outside of the conditions described,” the warning notice said.

An inspection found “bypasses and altered operation” of the mercury management system had “materially changed” emissions of the toxin compared to the environmental plan.

A spokeswoman for NOPSEMA said oil and gas companies were expected to “comply with their accepted environment plans and to ensure environmental impacts and risks are reduced to as low as reasonably practicable”.

But there was no safety concern for workers following the marine pollution incident.

Inpex senior vice president corporate Bill Townsend said the company “takes the matters raised seriously”.

“We are working constructively with the offshore regulator to address the matters identified in the (NOPSEMA notice) and further strengthen our systems and controls,” he said.

The company also said workers had been screened in line with Safe Work Australia guidance which “found mercury levels within the range typically observed in the general population”.

Mercury exposure can affect the brain, heart, kidneys, lungs, and immune system in humans. It accumulates in the environment and animals over time.