GardenSafe: Trace elements

Trace elements are substances that naturally occur in our environment in small quantities. They are elements on the periodic table and include metals (e.g., lead) and metalloids (e.g., arsenic). 

Some elements are beneficial to human and plant health at trace levels. Trace elements including copper, manganese, and zinc are essential for plant function. Deficiency will occur if concentrations are too low, and toxicity if concentrations are too high. Other trace elements, including lead and arsenic can be harmful to human health, even at low levels.

Previous research (Taylor et al. 2021) has shown that lead (Pb) is the most common trace element of concern in Australian garden soil. While modern paint and petrol no longer contain high levels of lead, the impact of their historical use remains a concern in some gardens today.

Houses built before 1970, are within 10 km of the Central Business District, near industrial processing facilities, or contain peeling paint are more likely to have elevated lead in their garden soil.

GardenSafe screens your garden soil for 8 trace elements. These were selected because they may be present in garden soil at concentrations that could impact human or environmental health, or they can influence how plants grow. A summary of each trace element assessed, and their common sources are provided below.

After sending us your soil samples, the concentration of trace elements in your soil will be measured using X-ray fluorescence spectrometry. A short report outlining the results from your garden will be emailed to you. This is paired with guidance on how to interpret your results using Australian guideline values and strategies to improve soil health and reduce your exposure to trace elements.

Trace elements

Trace element screening results from your garden are compared against the Australian Health Investigation Level guideline for residential gardens with accessible soil (HIL A).

This establishes the concentration above which further health investigation and evaluation should be considered, or alternative approaches to how you grow your veggies be implemented, such as using pots or raised beds with clean soil. Check out our webpage for guidance on how to reduce harm from contaminants.

For most garden soil samples, the HIL A guideline is the appropriate value to compare your results against (Table 1). Guidelines for other land use categories are provided in the National Environment Protection (Assessment of Site Contamination) Measure.

Table 1. Health Investigation Levels for trace elements in Australian soil (mg/kg)*

As - arsenic; Cd - cadmium; Cr – chromium**; Cu - copper; Mn - manganese; Ni - nickel; Pb - lead; Zn - zinc.

*From Table 1A(1) of the National Environment Protection (Assessment of Site Contamination) Measure; Schedule B (1), Guideline on Investigation Levels for Soil and Groundwater, 2013.

**Guideline is for hexavalent chromium (CrVI) but pXRF measures total Cr. See detail below.

Where:
HIL A = residential garden with accessible soil, including day care centres, preschools, and primary schools. Home grown produce equals less than 10% of fruit and vegetable intake, no poultry.

Chromium testing

Chromium can occur in different chemical states. This includes the metal state (Cr0) that is used for making steel, trivalent chromium (CrIII) that has low toxicity and is not easily absorbed into the body, and hexavalent chromium (CrVI) that has high toxicity and is a known carcinogen.

Your report contains the screening results for total chromium in your sample, meaning the concentration of all chromium states combined. However, the HIL A guideline value is for hexavalent chromium (CrVI) only.

It is unlikely that your sample contains all of one type of chromium. If the total chromium concentration in your sample exceeds the guideline for CrVI, you may consider further chromium testing (speciation) through an environmental consultant to determine if a risk is present. Or, you may implement alternative approaches to how you grow your veggies, such as using pots and raised beds filled with new soil from a reputable provider.

Interpreting your trace element results

The simplest way to interpret your trace element results is to ask: “Are the concentrations in my soil above or below the guideline provided?”.

If your soil is:

Above the guideline - Further investigation and risk assessment may be required. Reasonably practicable measures to remove or reduce the presence of, or your exposure to, that contaminant should be considered to reduce risk of adverse human or environmental health effects. Visist out page for reducing harm from contaminations for tips and guidance.

Approaching the guideline - Measures to reduce the presence of, or your exposure to, that contaminant should be considered.

Below the guideline - Carry on gardening. Keep in mind that good gardening practices like thoroughly washing hands and veggies, and mulching areas of exposed soil go a long way in reducing your exposure to soil and contaminants.

Map My Environment

Trace element screening data collected by GardenSafe will be displayed on the interactive platform: Map My Environment. The online tool combines work from other citizen science projects to improve environmental data accessibility and empower community to make informed decisions about their local environment.

You can use this online tool to explore our data and compare your screening results to other locations in the area.

To protect your privacy, technical controls, including a double jitter, are applied to the data, preventing personal information being used to spatially identify individuals or sample locations. View EPA's privacy policy for more information.

Jump to Map My Environment's global map, change the sample type to ‘soil’, and zoom to your suburb to get started.

Note: Only a qualified medical professional can advise how a contaminant could impact an individual’s health. Please see your doctor if you have any health concerns about soil contamination from trace elements.