Historic Pesticide Contamination

Agricultural and horticultural practises have included the use of various pesticides and agrichemicals.  Some of these chemicals can persist in the environment such that hazardous residues can build up and remain in soils.  In severe cases this may pose a direct hazard to people and the environment.  However, of greater concern is when land use change occurs, particularly the development of residential housing.  Land that is suitable for agriculture and horticulture may not be suitable for residential purposes. 

A wide variety of pesticides have been used in New Zealand over the last 100 years.  NZ studies have shown that some pesticide residues such as arsenic, lead, copper and DDT remain in the soil as contaminants. Pesticides containing these chemicals were used extensively in the Tasman District under Government registration until they were withdrawn from sale around 1975.  Some tobacco growers continued to use DDT up until about 1985.  

• Historic Pesticide Contamination Brochure

These pesticide residues are persistent in the environment and tend to bind tightly to the soil, most often in the top 10 cm.  Consequently they may be present in the soil as a contaminant long after they were applied.  The more soluble arsenic may leach slowly into underlying groundwater.

Generally, commercial horticultural crops grown on this soil comply with the level of residues permitted in the Food Standards Code as these particular contaminant residues are not taken up by most plants.  The exposure pathway of concern for human health is the ingestion of soil.  People are much more likely to ingest soil when in their home environment such as via home grown vegetables and, kids in particular, handling and playing in the soil.  Dairy and organic farming may also be restricted on impacted soils.

• Ministry for the Environment contaminated soil guidelines
• Australia and New Zealand Food Standards Code

Pre-1970s Orchard Land

Whilst all historic agricultural and horticultural land has the potential to be impacted, land that has historically been used for orcharding is considered particularly vulnerable.  Orcharding practises prior to the 1970s entailed the use of various pesticides and agrichemicals that persist in the environment.  A survey undertaken in 2003 found that concentrations of arsenic in soils under the trees and around the spray sheds and storage and handling areas at some historic orchards exceeded the Ministry for the Environment’s residential soil guidelines.

• Historic Pesticides Residues in Horticultural and Grazing Soils in the Tasman District Report

Council has mapped areas that were established orchards in mid 1975.  These properties are included in the Council’s Site Contamination Register.  Soil testing and, if necessary, remediation is required before such land can be used for residential purposes (e.g. subdivided for housing or construction of a second dwelling). 

The Council has prepared a set soil testing guidelines for assessing pre 1970s orchard land.  Council also maintains a list of accredited environmental consultants able to undertake such assessments.

• Soil sampling and assessment guidelines for horticultural sites in Tasman and Nelson Districts
• Framework for consultants undertaking assessment and reporting of potential soil contamination within Tasman District Council and Nelson City Council
• List of accredited environmental consultants to assess contaminated soils

Further Information

For more information contact Jenny Easton - Resource Scientist (Contaminants), Tasman District Council.