is known to "bioaccumulate" elements from irrigation water - but the
findings surprised rice researchers
lead levels in US rice imports
that rice imported to the US contained high levels of lead have been cast into
At a conference in April, researchers reported that commercially
available rice contained many times more lead than US food authorities deemed
The findings sparked international concern over imported rice.
But preliminary independent checks on the findings have failed to
replicate the results, and tests suggest the equipment used may have been to
The initial findings, revealed at a meeting of the American Chemical
Society, reported on tests of rice imported to the US from eight nations.
The team, led by Tsanangurayi Tongesayi of Monmouth University in New
Jersey, US, analysed rice using a technique called X-ray fluorescence.
reported results stand out as being orders of magnitude higher than normalâ€ť
Researchers claimed to have
found levels of lead exceeding by a factor between 20 and 40 the
"provisional total tolerable intake" for adults, set by the US Food
and Drug Administration. Their report suggested that untreated wastewater used
in irrigation was a likely cause.
Media reports, including that by BBC News, have caused concern
internationally, prompting two members of the European Parliament to raise the issue
formally and a follow-up
study by the Dutch food safety authority NVW.
However, attempts to replicate the results have found levels far below
those initially reported - between 6 and 12 parts per million (6,000 to 12,000
parts per billion).
Dr Tongesayi's team sent samples to another laboratory for analysis
using a different technique - that study recorded levels below one part per
The team then put on hold planned publication of the findings in the
Journal of Environmental Science and Health, for what Dr Tongesayi told BBC
News was a "data verification exercise". The American Chemical
Society was asked to remove the press release on the work from its website.
"The most important issue for me at this point is to make sure the
data is accurate," Dr Tongesayi told BBC News in late April. "If it
is not accurate, we will obviously not publish the paper."
The team subsequently sent the instrument used in the study back to its
manufacturer, which has since reported that the machine has calibration
The Dutch authorities' independent study of 26 samples of rice imported
from Asian nations found average levels of seven parts per billion - a
thousandth of those found in the original study - and with no samples above the
EU limit of 200 parts per billion.
Dr Tongesayi's findings also stand in stark contrast to prior published
research on lead in rice, most of which have been established using a technique
called mass spectrometry, which allows for more precision.
The International Rice Research Institute (IRRI) said in a blog post that "even where the soil is contaminated with a lead spill, a
number of studies have shown that rice plants do not take up a significant
amount of lead and move it to the grains".
Alex Waugh of the UK's Rice Association said that "in terms of work
undertaken throughout Europe and the USA on rice of multiple origins, Dr
Tongesayi's reported results stand out as being orders of magnitude higher than
"This in itself ought to be enough to raise questions about whether
his data are correct," he told BBC News.
In 2010, the European Food Safety Authority published a reportoutlining analysis
of 612 rice samples from the EU, finding average levels of just a few tens of
parts per billion.
An extensive study
in 2012 by US magazine Consumer Reports, including rice and rice-based products
such as rice cakes and drinks available in the US, measured lead levels even
lower, with a majority of samples measuring less than five parts per billion.
The Federation of European Rice Millers told BBC News that "there
is no published evidence of rice containing the levels of lead of [even] the
same order of magnitude reported by Dr Tongesayi, and consequently no evidence
of 'harmful levels' of lead in rice on the European market".
Dr Tongesayi told BBC News he was determined to reconcile his initial
findings with the outcomes of subsequent analyses of his samples by other
means, including the mass spectrometry method.
Sarah Beebout, a soil scientist with the IRRI, said: "I will be
surprised if the independent analysis confirms these apparently anomalous
results, but that will be a good starting point for scientific discussion and
investigation if it happens."