Why You Should Test Your Soil

What contaminants are in New Zealand soil

Some of the more common contaminants in soil include asbestos and heavy metals such as arsenic, cadmium, chromium, copper, lead, mercury, nickel and zinc. These can all impact human health and some can be fatal to pets. Pesticides like glyphosate and DDT are also a concern. 

People and pets can be affected by chemicals and contaminants in soil through:

Ingestion: This commonly occurs when eating fruit and vegetables grown in contaminated soil. Hand to mouth ingestion also happens when children play in, or help you in the garden, dogs eat buried bones, chickens forage for food and bugs, and toddlers and babies put dirty toys in their mouths.

Inhalation: Breathing in/inhaling soil dust when digging the garden or even just in windy conditions.

Dermal absorption: This happens when your skin is in direct contact with contaminated soil and when soil gets caught under your nails.

How do contaminants get in your soil?

There are a range of ways that contaminants can get in or have gotten into your soil.

Historical horticulture and agriculture

The land many of our houses are built on were once used for orchards, market gardens and farms. These industries frequently spray pesticides to control weeds, bugs and insects, and fertilisers to promote growth. Pesticides are effective in controlling pests and most of the sprays that are used today break down quickly, however some of the sprays used years ago we now know are toxic to humans and the environment, and many of these chemicals can still be found in your backyard today. Cadmium rich phosphate fertilisers have a long-standing history of use within New Zealand farms and whilst the phosphate gets regularly uptaken by the grass, some of the cadmium gets left behind and accumulates in the soil.

Lead-based paint

Paint used until 1965 on homes in New Zealand commonly contained 10-20% lead and up to 1% lead until 1997. When this paint degrades or when the house or building is maintained, paint flakes and paint dust spread into the soil around the house which then becomes contaminated with lead.

Treated timber

Decks, raised garden bed surrounds and excess or dumped building materials are all likely to have been made with treated timber. The chemicals used to treat the timber can leach into the ground and contaminate the soil around them. 

Unknown fill

"Free Cleanfill" is a common occurrence in social media market places. But is it really clean? Do you know the history of where that soil came from? Most soil contamination isn't visible so just because it looks 'clean' doesn't mean that it is.

Sheep dipping

In addition to use in horticulture, the farming industry used pesticides such as dieldrin and arsenic as sheep dipping chemicals to treat parasites on sheep and other livestock from the 1940s - 1980s. The persistent chemicals used in historic sheep dips either do not break down at all or break down very slowly once they enter the soil and can be considered hazardous to human health. Due to their persistence in soil, sheep dip pesticides used pre 1980, can still be found within soils today; presenting a risk to human health for years to come.

Killing weeds

Glyphosate is a pesticide commonly used for killing weeds. It is a 'non selective' herbicide, meaning it will kill most plants, not just weeds. Glyphosate is a controversial chemical with vigorous debate around the effect of the chemical on humans and the environment, and its persistence in soil.    

Do we still use these chemicals and contaminants now?

Eventually it was discovered that many pesticides were hazardous to humans and to the environment and that the chemicals either didn’t break down or broke down so slowly that they remained in the soil for many, many years. Hence most persistent pesticide sprays were banned in New Zealand by 1990. 

Horticultural and agricultural sites

Pesticide use on horticultural sites is still quite a common practice, but the type of pesticides used have changed significantly over time. Most modern sprays used today are not persistent in the environment and break down quickly once used. Cadmium rich phosphate fertilisers are still used within New Zealand, however the industry is working at lowering the level of cadmium they contain.

Lead-based paint

By 1965, the maximum permitted lead level in paint was reduced to 1%. In 1997 it was further reduced to 0.1%. Commercial paints (the aviation industry for example) still contain varying levels of lead due to its beneficial properties that make it hardwearing, moisture resistant etc. Any house built pre 1965 is likely to contain high levels of lead in the underlying paint layers and has the potential to contain lead within the surrounding soils. 

Treated timber

Treated timber containing copper, chromium and arsenic among other chemicals is still used in construction today. 

DDT and Dieldrin

DDT and dieldrin were both banned in New Zealand once the environmental impacts were understood, however due to the length of time these chemicals take to break down they are still commonly found in our backyards today.


Glyphosate is still currently used under a multitude of brand names in New Zealand. Roundup is probably the most well known brand of weed-killer that includes glyphosate as one of its ingredients.

What are the health risks from chemicals or contaminants that might be in my soil?

The health effects that can occur can vary depending on what chemicals or contaminants are present and at what levels. We recommend you visit The Ministry of Health & Ministry for the Environment websites for more information about soil contaminants and how they can affect you.

How to test your soil and find out if it is contaminated

If you think your soil may be contaminated with one or more of the contaminants listed above, you can purchase DIY Soil Test Kits here.

If you need a more comprehensive investigation or specialist testing such as a Preliminary Site Investigation or a Detailed Site Investigation, contact EWB Consultants to discuss your options.