Study highlights need for subdivision soil testing
Agrichemical study highlights need for soil testing before subdividing land for housing
For immediate release: Monday 4 April 2005
A comprehensive study of agrichemical residues in Bay of Plenty soils has highlighted the possible need for soil testing of horticultural sites proposed for residential subdivision.
The study was managed by Environment Bay of Plenty as a joint project between the regional council, Tauranga City Council and the district councils of Western Bay of Plenty, Rotorua, Whakatane and Opotiki.
Paul Dell, Environment Bay of Plenty’s group manager regulation and resource management, says the study detected higher background levels of some chemicals, particularly on old horticultural sites, which required more intensive spray regimes and different sprays than today. But the degree of elevation was “significantly less” than those found in a similar study in Auckland, he explains.
The study involved sampling nearly 130 horticultural and agricultural sites in the region for background agrichemical residue. Its aim was to find out whether Bay of Plenty soils have elevated levels of persistent agrichemicals and whether these levels pose a significant risk to any future land use.
“Many land uses in the past (mainly pre-1975) required the use of chemicals that have since been prohibited but are causing concerns internationally because of their persistence in the soils and the associated health risks,” Mr Dell says. “With much of our future residential development coming from ‘greenfield’ land or land that is currently used for horticultural or agricultural purposes, we wanted to be sure that the land was suitable for the new end use and that such developments did not bring with them any potential human or environmental health risks.”
The study set conservative levels for risk to both human health and the environment, basing trigger values for human health on a lifetime exposure of over 70 years.
While a number of sites had residue levels above the guidelines, none were at levels that flagged major health or environmental concerns, Mr Dell explains. More than half the sites did not show any elevated levels of chemicals at all. Three chemicals, copper, arsenic and DDT, posed the greatest risk, exceeding the guidelines on the highest number of sites. A few sites also exceeded lead, zinc or cadmium guidelines.
Mr Dell says the findings reinforce the need for caution and site-specific evaluation of potential contamination when subdivision applications are being considered on old horticultural properties. It will likely result in some changes to the process that takes place before a subdivision is approved by the relevant district council.
Environment Bay of Plenty and territorial local authorities will be developing appropriate policy for the assessment of future subdivisions.
Mr Dell wants to thank the landowners who agreed to take part in the study. Individual results have been sent to participants and will remain confidential to them.
You can view the study report on www.envbop.govt.nz or at Environment Bay of Plenty offices in Tauranga, Rotorua and Whakatane.