![Some phosphine testing at delivery sites is done using grain gathered with a probe. Photo by Gregor Heard. Some phosphine testing at delivery sites is done using grain gathered with a probe. Photo by Gregor Heard.](/images/transform/v1/crop/frm/5Q2j7ezUfQBfUJsaqK3gfB/1c1fbcfb-a18f-4100-932e-f41045d723e8.JPG/r0_40_6000_3693_w1200_h678_fmax.jpg)
Phosphine is by far and away the most important grain storage fumigation product in the arsenal of Australian bulk handlers and farmers storing grain on-farm.
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However, the industry is being warned to prepare for changing delivery standards, with reports of bulk handling sites rejecting loads of grain for high levels of phosphine.
Manoj Nayak, Queensland Department of Agriculture and Fisheries (DAF) grain storage specialist said there was a plan to reduce the allowable levels of phosphine from 0.3 parts per million to 0.05ppm on a threshold limit value / time weighted average (TLV-TWA) basis in order to protect workforces exposed to the chemical which would impact how growers use the product.
"The industry needs to get prepared to manage this challenging new level, only a sixth of the existing standard, and not have grain rejected," Dr Nayak said.
He said the issue was further compounded by ambiguous measurement standards, with some results done from spear testing of grain and others measuring levels in the air on a TWA basis.
"There are discrepancies between the grain under the surface and the grain on the surface due to the way the phosphine moves through the grain."
"It is a complex matter, the grain sorbing the gas during a fumigation and desorbing back to the atmosphere afterwards makes it difficult to know when it is safe to move the grain."
Speaking during a Grains Research and Development Corporation (GRDC) webinar Dr Nayak said research into aeration and its impact into phosphine levels had been interesting.
Current labels recommend not less than five days for natural airflow, between two and five days with throughflow and natural airflow and not less than one day with fan forced airflow, done with a flash proof fan.
He said in trial work, constant fan flow pushed levels down below current receival levels as quickly as day one, the readings jumped around but stayed below the 0.3ppm level.
However, a trial using a fan on two hours, off two hours, designed to save power did not have such success.
"It was a disaster," Dr Nayak said.
"In the modelling phosphine levels remained above 0.3ppm for the entire first five days of the trial and even after that they were very close to the level."
He said passive ventilation was also inadequate.
"It did not bring down the levels fast enough."
"Even if the passive or the two on, two off treatments are on the label, I couldn't recommend it."
Meanwhile, work is also going to look at the best way to fumigate silo bags, which are an important part of many growers' grain storage strategies.
Mark Earles, of the GRDC's grain storage extension project, said it could be time consuming to get the grain down below the 0.3ppm level but said it was something being researcher.
"The levels fell quickly from their initial levels, but the last little bit took some time."
"Having the bags in good working order is important to start with."
Both Dr Nayak and Mr Earles recommended using a low range phosphine meter to test gas levels have cleared before outloading, saying it was the surest way to ensure delivery limits are met, and avoid rejected loads.
Dr Nayak said work would continue on trying to come up with a clearance method for the new standards.
"In the meantime, we will continue working with industry to attempt to develop a safe and practical clearance test method before the new 0.05ppm TWA comes into effect."