BlueScope Steel Limited has been fined $30,000 for allegedly failing to comply with dioxin air emission limits on six occasions in March and April 2020.
The NSW Environment Protection Authority (EPA) fine comes after BlueScope shut down part of the Port Kembla steelworks in May after high levels of air pollution were detected on four different dates.
BlueScope recorded the limit exceedances emissions "for this potentially harmful substance" between 26 March and 28 April during major maintenance activities at the Sinter Plant Waste Gas Cleaning Plant.
EPA regulatory operations metropolitan director Giselle Howard said BlueScope responded to the exceedances by completing air emissions modelling and engaging an independent consultant to undertake a health assessment of the elevated emissions.
"High levels of dioxins can be extremely harmful to human health, on this occasion air emissions modelling and a health assessment have shown that community impacts were unlikely from the emissions," Ms Howard said.
"The local community has an expectation that every effort must be made to ensure that licensees will comply with their licence requirements and have best practice controls in place to protect people and the environment."
At the time a BlueScope spokesman said: "BlueScope immediately notified the EPA of the exceedance and was instructed by the EPA to increase the frequency of testing for dioxins/furans from weekly to daily".
BlueScope has also been directed to complete several new Pollution Reduction Programs and is also undertaking additional investigations to understand the root cause of the elevated dioxin emissions.