The Customs Service has reviewed its approach to fumigant detection following a study which found some containers imported into New Zealand had concentrations more than 100 times above safety guidelines.
The study was carried out at the Port of Tauranga from February to June 2011.
The details have just been released following a request under the Official Information Act.
Tests were done for nine fumigants including formaldehyde, hydrogen cyanide and methyl bromide. All three carry health warnings.
Approximately 20% of the air samples collected had concentrations of fumigants above the safe level and in many cases several different kinds of fumigant were detected.
The Customs Service says of the 519 containers involved in the study, only two displayed the correct fumigant signs.
Customs Service spokesperson David Campbell says the study has led to improvements to health and safety processes relating to the handling of containers.
The service is now ensuring suitable ventilation equipment is used at all its container inspection facilities.
Mr Campbell says the information was shared with industry partners in May last year, including the Ministry of Business and Innovation and the Ministry for Primary Industries.