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Past horticultural activity in residential areas

Background

The Auckland region has a long history of horticultural activity, such as market gardens, orchards, glasshouses and vineyards. In Auckland City's case, that history is far less extensive but some parts of the city were used for horticultural purposes in the 1940s, 1950s and in a few cases later than that.

In 2001, the Auckland Regional Council and the Auckland District Health Board undertook a research project into the potential effect of past horticultural activity on soil.

The study aimed to identify whether regular activities on land used for horticulture, such as weed spraying and the use of pesticides, left a build up of different chemicals in the soil.

The study involved sampling 43 horticultural and agricultural sites in the Auckland region. Only one site within Auckland City's boundaries was tested.

The study concluded that past horticultural activity resulted in comparatively higher levels of contaminants on less than half (approximately 45 per cent) of the sites that were tested. The remainder of the sites showed acceptable levels. The site tested in Auckland City showed acceptable levels. A copy of the report is available on the Auckland Regional Council website.

After receiving this report, Auckland City initiated a study to identify any properties within Auckland City's boundaries that may in the past have been used for horticultural activity. The study did not involve sampling. Instead, old aerial photographs from the 1940s, 1950s and 1960s were used to identify areas of land where horticultural activity may have taken place. These areas were then identified on a modern map of the developed isthmus.

Auckland City found that the properties of 4,872 residential owners may possibly be on land previously used for horticulture.

The information Auckland City has does not say that a property is contaminated. This can only be determined by individual testing of the soil on the property. All we are saying is that Auckland City considers that a property was historically used for horticultural purposes.

Download the following map for an indication of the areas with potentially affected sites. Please note that the map does not identify specific properties.

Historical residential horticultural sites map (3mb) PDF

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Information on LIMs

In late 2004, at the request of Auckland City, the Ministry for the Environment approached the Crown Law Office for clarification of councils' responsibilities to disclose information about past horticultural land use on LIMs. Auckland City received the Crown Law opinion in late December 2004.

The Crown Law Office agreed that Auckland City had acted lawfully by using its discretion to put the information on LIMs, but pointed out other ways it could be made public.

Immediately after receiving the opinion, Auckland City decided it would not proceed with putting the information on the LIMs of affected properties.

Pilot testing programme

Early in 2005, the ARC applied to the Ministry for the Environment for funding to undertake a soil-testing programme in Auckland city. This programme was to look at the extent to which the passing of time and subdivision on the land can dilute the amount of pesticides in the soil.

The application for funding was approved and Auckland City and the ARC began the process of identifying properties that were suitable to include in the pilot programme. Not all properties were suitable, as we needed properties that were the site of former glasshouses or spray sheds. We knew that these sites were likely to have the highest levels of contamination so if the results of the pilot showed contamination levels at these sites were within guidelines, then other sites could reasonably be assumed to also fall within guidelines.

We wrote to around 100 owners of suitable properties but less than ten per cent was willing to take part. This means that we do not have enough properties to allow us to undertake a scientifically valid pilot testing programme.

The ARC is continuing work in the Avondale area to identify sites that had spray sheds or glasshouses on the property and will approach owners seeking their cooperation in a pilot testing progamme, which will be funded by the Ministry for the Environment and lead by the ARC.

Private soil testing and development

If homeowners wish to undertake their own soil testing, they should talk to an experienced environmental soil-testing consultant. However, homeowners should talk to Auckland City in the first instance for advice on what tests need to be done and how the testing should be undertaken. Auckland City can liaise with the consultant where required. If a property owner chooses to test their land, it is the responsibility of the property owner to pay for testing.

Some subdivisions and developments, for example those involving major earthworks or a significant increase in density of people living on the site, may need some form of soil assessment. Property owners investigating these options should call Auckland City to discuss the need for any assessment.

If testing undertaken by an individual property owner comes up clear, property owners should contact us to arrange for the results to be put on record.

If testing confirms that the soil is contaminated, the property owner must call Auckland City. The LIM for the property concerned will be tagged with the information. The environmental consultant who tested the soil will suggest a range of options including remediation.

Health concerns

We do not even know if there is residual contamination in the soil at the affected properties.

All we know is that the properties may in the past have been used for horticultural purposes.

This information describes the health concerns involved, and gives basic advice on what people living in these properties can do to minimise exposure to contaminants in soil.

The information is provided by the Auckland District Health Board. If you would like to discuss any health concerns, contact the Auckland District Health Board on (09) 262 1855.

Exposure
Guideline levels - what they mean
Chemicals used
Advice for occupiers
Reducing exposure from the garden

Exposure

A small proportion of the nearly 5000 Auckland properties built on land previously used for horticulture may have residues of pesticides and other chemicals above guideline levels.

The current contaminated land situation may have lead to long term, low level chemical exposure in those sites which have been used as orchards or for glasshouses or chemical storage sheds. Some properties will be more likely than others to be affected because of the type of activities (for example glasshouses, chemical storage sheds or orchards).

The main exposure routes include soil and dust ingestion, contact with bare soil and uptake of chemicals into food produced on the property. People normally ingest around 50-100 milligrams of soil and dust a day, for example eating after getting soil or dust on hands. Young children are of concern as they take in more soil than adults through such things as playing outside, putting toys in their mouths and crawling on the floor in areas where soil and dust have been brought into the house on shoes.

People could be exposed to some of these chemicals from multiple sources, so the chemicals in the soil will be contributing to total exposure, but may not be the most important source.

For example, the most common source of exposure to lead in children remains through lead-based paint dust that is created during renovations of older houses, and soil lead is small in comparison.

In many properties, soil has already been removed, so would not be of concern, unless replaced by other contaminated soil.

Guideline levels - what they mean

Results from soil testing usually refer to a guideline level. These are usually worked out based on the lowest level where a life time exposure might have an effect on health, with an additional safety margin included (often a factor of 10 or 100). Guideline levels reflect current understanding, so may change over time.

The majority of former horticultural land in Auckland City is likely to have levels of chemicals below the guidelines. For land with chemical levels at or slightly above the guideline levels, only the basic measures described later would be recommended. Only land with very high levels would need soil remediation or replacement.

Chemicals used

The health effects described below include those from high exposures which may not be relevant to the sorts of levels of exposure people will have from even the most contaminated properties that will be found.

Lead	Lead was used in an insecticide (lead arsenate) until the 1950s to 1960s, and in paint used on glasshouses, sheds and houses before the 1970s. Petrol was also an important source of lead before the 1990s. In Auckland, the main concern is children being exposed to lead from old lead paint, especially from renovating old houses. Soil lead from former horticultural sites another source, but will usually be less important than old house paint. Lead mainly affects the nervous system and kidneys. Minimising children's exposure to lead from all sources is important as exposure to lead can affect the development of children's brains and nervous systems. Children also absorb lead more effectively than adults do.
DDT and Dieldrin	These were insecticides used until the 1970s. They are "organochlorine" chemicals, which persist in the environment and accumulate in animals (including humans) mostly through the food chain. The health concerns from long term exposure include effects on hormone and reproductive systems and possibly cancer. Most exposure is through food, but soil could be another source. Overall exposure to these chemicals is decreasing over time (see the Ministry of Health's website www.moh.govt.nz, search for "DDT"). The Ministry for the Environment website also has information on organochlorines (www.mfe.govt.nz).
Arsenic	Arsenic was used in lead arsenate insecticides and is still used as a timber preservative. Soil and treated timber could lead to low-level exposure. High levels of arsenic over a long period can increase the risk of some cancers, especially skin cancer. This is unlikely in the current situation.
Copper	Copper is needed by the body in small quantities, but exposure to very high levels can cause nausea, diarrhoea and vomiting. Long term, high exposure to copper may have adverse effects on the liver, blood, pancreas and lungs.

Advice for occupiers

For properties where contamination is likely to be low, washing hands after playing or working in the garden and discouraging children from eating soil are sufficient precautions.

The following advice is relevant if there is known contamination. Ways to minimise exposure to contaminants in soil include:

maintaining a good grass cover on lawns and cover gardens with bark. This will act as a soil barrier and minimise exposure to bare soil
washing hands after handling soil
discouraging young children from eating soil
washing hands before eating and drinking and smoking
removing shoes before entering the house. This will help to prevent contaminated soil from being tracked into homes.
washing door mats regularly to remove contaminated soil
regularly vacuuming and mopping children's indoor play areas
building sandpits above ground and filling with clean sand
minimise activities which expose bare soil.

Reducing exposure from the garden

Ways of reducing exposure through vegetable gardens and gardening:

wash hands thoroughly before eating and drinking
remove soiled clothes and shoes worn for gardening before entering the house
wash clothes used for gardening separately
test the soil pH before planting a vegetable garden. Plants will take up less copper, cadmium, lead and zinc from soils with a neutral pH. Testing soil in a vegetable patch for the chemicals should be considered but is expensive.
increase the organic matter content of the soil by adding animal manures and compost
raise the soil pH using lime. This is not advised if arsenic is the contaminant of concern.
Replace contaminated soil and/or grow vegetables in containers or raised beds filled with clean soil
use a soil barrier between uncontaminated soil and contaminated soil
washing and peel vegetables to remove soil particles
plant suitable vegetable crops. Fruiting vegetables (for example tomatoes and beans) generally take up lower amounts of contaminants than root (potatoes) and leafy (for example lettuce and silverbeet) crops. Some varieties of the curcubit (for example zucchini and pumpkin) family have been shown to take up organochlorine compounds from contaminated soil.
avoid composting plant material grown on the site
dampen down soil before digging and weeding to reduce dust

Parks and reserves

The desktop study undertaken by Auckland City identified 17 parks that may have been used in the past for horticultural purposes. All 17 of these parks were tested. Twelve parks were found to be clear of any residues. These 12 parks are:

Meadowbank Reserve, Meadowbank
Tahapa Reserve, Meadowbank
Glendowie Park, Glendowie
Peterson Reserve, Panmure
Boundary Reserve, Dunkirk Reserve, Johnson Reserve, Riversdale Reserve and Torino Reserve, Panmure (these reserves are adjacent to each other)
Blockhouse Bay Beach Reserve, Blockhouse Bay
Blockhouse Bay Recreational Reserve, Blockhouse Bay
Auckland Domain, central Auckland
Tony Segedin Esplanade Reserve, Avondale
Margaret Griffen Park, Mt Roskill
Mt Wellington War Memorial Reserve, Mt Wellington
Point England Reserve, Pt England

The remaining five parks were found to have isolated areas of pesticide residue. All five parks remain open and are considered safe for recreational activity.

These parks are:

Park	Details of action taken
Mount Albert War Memorial Reserve, Mount Albert	Mount Albert War Memorial Reserve showed slightly elevated levels of lead. Remediation has already been undertaken.
Orakei Sports Domain, Orakei	Two sample areas in the vicinity of some old sheds have elevated levels of lead. Further targeted soil testing and analysis will be undertaken.
Churchill Park, Glendowie	There are elevated levels of some substances in the vicinity of some former sheds. In this area, elevated levels of arsenic and lead were evident. Further targeted soil testing and analysis will be undertaken. The residues are evident in areas where recreational activity is unlikely.
Riversdale Reserve, Avondale	There are elevated levels of copper in five samples taken in the open field area. One of these samples also just exceeded the guideline for DDT. Three samples at the site of former sheds had elevated levels of copper, lead, DDT and arsenic. Further targeted soil testing and analysis will be undertaken.
Avondale Canal Reserve, Avondale	One sample had marginally elevated levels of lead. Further targeted soil testing and analysis will be undertaken.

Other council areas

The assessment of the effects on soil from past horticultural activity is a regional issue.

For enquiries about sites outside Auckland City's boundaries contact the relevant local council.

North Shore City Council:	486-8400
Manukau City Council:	263-7100
Waitakere City Council:	839-0400
Rodney District Council:	(09)426-5169
Franklin District Council:	(09)237-1300