The fertiliser manufacturer Ballance Agri-Nutrients has been fined $60,000 for discharging sulphur dioxide into the air in Tauranga.
The incident occurred in May last year and a company investigation shows it was due to human error.
Tauranga port workers near the Ballance plant suffered breathing difficulties, watering eyes, sore throats and coughing from the fumes.
The Fire Service traced the smell back to Ballance Agri Nutrients and notified the council.
Bay of Plenty Regional Council took the company to court for breaches of the Resource Management Act.
Judge Jeff Smith said the company had enhanced its safety systems following the incident, but the fine showed the importance of making sure environmental risks are managed when they could significantly affect people's health.