Shining gum plantations in Tasmania's north-east have been found to be highly toxic and could be responsible for rare cancers in humans and animals and widespread facial tumours amongst Tasmanian Devils.

Friends of the Earth and Friends of Gippsland Bush want the State Government and Hancock Victorian Plantations (HVP), which owns 5600 hectares of shining gum in the Strzelecki Ranges, to test the Victorian trees and downstream waterways for similar toxins.

The groups believe the plantation company could be using `genetically improved' planting techniques similar to that of the Tasmanian timber industry but HVP says it's a natural process.

Friends of Gippsland Bush secretary Susie Zent said she was concerned with the possible toxicity of local shining gum leaves.

``They (HVP) have not scientifically proven or conducted long-term research into the effect of planting a monoculture of an altered gum species in our area,'' Ms Zent said.

``It doesn't matter how they `genetically improve' the trees, if they're toxic that's a big concern.''

HVP external relations manager Steve Wentworth said the term `genetically improved' was misleading and implied the trees were genetically modified, but the company's process was natural.

``I would call it tree selection. We go out to native stands of shining gum and collect trees from the seeds we think would make the best trees for our purposes,'' Mr Wentworth said.

``The seeds are grown in a seed orchard and seeds pollinate each other naturally.

``The type of offspring from those trees tends to be taller, faster-growing, higher-volume trees.''

Mr Wentworth said he was unsure whether this process was the same as the Tasmanian case and the company would keep abreast of any interstate developments.

A spokesman for Environment Minister Gavin Jennings did not respond in time for print.