Metal detectors: a new geochemical atlas for Aotearoa

Thanks in part to experts in soil contamination from Manaaki Whenua, Aotearoa New Zealand now has its first ever Geochemical Atlas, providing a baseline of concentrations of elements in our near-surface soil.

Manaaki Whenua senior researchers Dr Jo Cavanagh and Dr Pierre Roudier worked with a team from GNS Science and the University of Auckland to measure the concentrations of 65 different elements in our soils, with analysis drawn from more than 800 samples taken from within the top 20 cm of soil. The atlas presents the results using maps, showing the changes in concentration in each element across the country from Cape Reinga to Rakiura Stewart Island.

“This information helps identify where trace elements may need to be added to enhance productivity or improve the nutritional quality of food crops for livestock and people,” says Jo.

“For example, selenium is an essential trace element, and the atlas shows many New Zealand soils are low in selenium, particularly in the central North Island, Otago, Canterbury and Marlborough.”

Several of the elements included in the atlas are metals that can be hazardous to human health, including arsenic, boron, cadmium, chromium, copper, mercury, nickel, lead, and zinc. The occurrence of these metals in the soil varies due to differences in underlying rock types, environmental conditions and human influence.

Jo says knowing the concentrations of metals in our soils for the first time nationally helps us understand where human activities have changed naturally occurring concentrations, and allows us to monitor changes and mitigate their potential impact on human health and the environment.

The maps show elevated levels of lead and arsenic in several urban centres, but this is not unexpected, says GNS Science Geologist Mark Rattenbury. “This is a known phenomenon in cities worldwide, with possible sources including pollution from industrial processes, leaded petrol from our past, disposal of fossil fuel residues and household refuse, and the deterioration and removal of lead-containing paints from older houses.”

Note: the maps cannot be used to pinpoint element concentrations for individual properties.

Downloads and links

• Geochemical atlas of Aotearoa New Zealand (GNS Science Online Store)
• New atlas maps metals and other elements across Aotearoa’s soils
• Soil contaminants