Every few minutes, a logging truck rumbles through the gates at the Port of Tauranga. More logs arrive by train.  The wharves at Mount Maunganui are covered in huge stacks - there are so many logs they've had to store them in a yard nearby.

All this wood - 5.5 million tonnes of timber went through the port last year - has brought jobs and industry to the area. It's also brought methyl bromide. Loads of it.

The gas is an extremely effective killer of all organisms and is used in small quantities to fumigate imported fruit, vegetables and other products. But by far the biggest users are timber exporters. In 2016, 220 tonnes of the toxic, ozone-depleting gas was administered to logs at the Port of Tauranga to kill insects prior to export.

Another 250 tonnes was used at Northport near Whangarei and 70 tonnes at Napier Port - making New Zealand the world's fifth biggest user of methyl bromide and by far the biggest per capita.

Our consumption of the fumigant has rocketed from less than 100 tonnes in the early 2000s to around 600 tonnes today, mirroring a timber boom - log exports have tripled since 2008 and are now worth $2.7 billion.