An aerial photo over Avonside Drive in the residential red zone.

Canterbury University researchers are warning against using the residential red zone for food production.

Environmental chemists Professor Brett Robinson and Associate Professor Sally Gaw said urban soils often contained contaminants such as lead, arsenic, and DDT.

"Recent investigations have shown that many Christchurch soils, including those in the red zone, were above regulatory limits for these contaminants," the pair said in a media statement.

SUPPLIED Environmental chemist Associate Professor Dr Sally Gaw.

Regenerate Christchurch recently released a report saying livestock grazing and fodder production were options being considered for the red zone.

READ MORE: Cow fodder 'highest and best' use of cleared suburban Christchurch land

Two of the organisation's 10 proposals for the area include "productive land uses", which could include dairy grazing.

Gaw said the land could be checked and cleared of contaminants, but it likely wouldn't be worth it.

"There would need to be an awful lot of investigation. They'd really need to know what was in there first.

"Urban areas, it's just damaged land, it's land that's been used for other things that probably precludes it from being used for productive use."

She said contaminants were often found when overseas trading partners analysed food, putting the country's reputation at risk.

Gaw said fruit crops might be fine, but not food that has contact with the soil.

She said it wasn't just the red zone, but any city area that could be contaminated.

"It does always worry me when people talk about using urban areas for food production.

"Free range chickens would be equally problematic."

Gaw said people growing food in their back yards could use raised garden beds to be safe.

Robinson and Gaw's statement said contaminant "hot spots" were common but were difficult to locate, and could lead to toxins entering the food chain.

"Vegetables, particularly root crops and leafy greens, are also at risk from these contaminants," Gaw said.

"We recommend that the land not be used for grazing, fodder production or vegetable crops as a precautionary measure," Robinson said.