An investigation has found there is insufficient evidence to support claims methyl bromide exposure was to blame for four Port of Tauranga workers falling ill.

On March 8, four stevedore staff from ISO Limited were working about 100m from where stacks of logs were being fumigated with methyl bromide by Genera Ltd staff.

Fumigating company, Genera Ltd, was contracted by a number of parties to carry of methyl bromide fumigation of import containers, export containers and export timber as part of quarantine, import and export requirements.

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The workers later suffered symptoms including wheezing, abdominal pain, nausea, vomiting and general lethargy. All four visited hospital.

One of the workers was admitted overnight and three were treated and discharged.

A report by the Bay of Plenty Regional Council found there was insufficient evidence to prove beyond reasonable doubt that the complainants were affected as a result of the fumigation activity.

The investigation took into account an explanation from Genera on what occurred on March 8, meteorological information including wind speed and direction data, video surveillance footage from the Port of Tauranga, talks with workers affected in the incident and gaining their medical records and commissioning reports from a consultant toxicologist and an air modeller.

However, the investigation found a number of compliance issues and four abatement notices had been issued to Genera.

The notices were issued because Genera's monitoring equipment was not downwind at the nearest port boundary, the company had not submitted a plan of fumigation areas to be approved by the council, at times log fumigation had been carried out within the 100m limit of the boundary and the council had not been advised within 24 hours of the complaint.

Genera's chief operating officer, Matt Hill, said WorkSafe and the Bay of Plenty Regional Council found the cause of the workers' illness not to be because of methyl bromide, "which was good".

Hill said the company was "quite surprised" with the abatement notices issued by the council.

The company was looking to take advice and had not ruled out appealing the notices, Hill said.

Methyl bromide

● Highly toxic gas
● Is colourless, odourless and non-flammable
● Is ozone-depleting
● Has been used as a pesticide
● Has been phased out of use in many countries
● Linked to motor-neuron disease