Doubts over MAFF reassurance on metal contamination of vegetables

Reassuring conclusions about dietary intakes of metals have been drawn by the Ministry of Agriculture, Fisheries and Food (MAFF) following a study of metal contamination of vegetables and milk produced on farms near industrial sites.1 But there is doubt about their validity because of MAFF's choice of industrial processes and the fact that most of the vegetable-growing sites were too remote to be affected by fall-out from low-level emissions - though even so metal contamination of some vegetables was above proposed EC limits.

Vegetables and cows' milk were analysed for 13 metals and other elements. The milk samples were taken in 1994 for a survey of dioxins in milk produced near 28 industrial sites. The vegetable samples were taken in 1996 from 40 allotments, pick-your-own farms and farm shops near major industrial sources of heavy metals in Redcar, Bristol, Newcastle, Rotherham and the Team Valley.

Contaminant levels in milk were not out of line with results of national surveys carried out by MAFF, with one exception. This was milk from a farm at an undisclosed location which contained 144µg/kg of lead and 9µg/kg of antimony - more than ten times the mean levels found in the 1994 total diet study. The farm is no longer producing milk for human consumption, and milk contamination on adjacent farms was within the normal national range.

In contrast, levels of arsenic, cadmium, cobalt, mercury and lead were found to be higher - often considerably so - in some vegetables than in other MAFF national surveys. Mean concentrations of both lead and cadmium in runner beans, for example, were more than ten times higher than in a recent survey. Mean levels of lead and mercury in potatoes were five and two times, respectively, above the levels found in the 1994 total diet study. Other vegetables with elevated concentrations of these metals included cabbage, carrots, kale and onions.

To assess possible risks to consumers, MAFF used the sum of the two highest upper range - 97.5 percentile - contaminant intakes from individual local crops plus the mean intakes for any remaining local crops. Average intakes from the rest of the diet as calculated in the 1994 total diet study were then added to these figures to give the total dietary intake.

The result of most concern was for cadmium. The worst case total daily intake of this metal was 65µg per person - above the tolerable weekly intake of 60µg recommended by the World Health Organization and Food and Agriculture Organization, and more than double the upper range intake of 25µg estimated from the 1994 national study.

The worst case daily intake for lead was, at 94µg per person, also well above the upper range of 38µg calculated from the 1994 national study. In this case, however, it was well within the internationally recommended value of 214µg.

Statutory or guideline limits on arsenic, lead, tin and copper in food have been set in the UK, and none of the vegetable samples exceeded these. However, maximum concentrations of lead in runner beans, cabbage, carrots and leeks, as well as mean levels of lead in runner beans, were all in excess of limits proposed in last year's draft EC Regulation on contaminants in food offered for retail sale. The maximum levels of cadmium in leeks and potatoes also exceeded the proposed EC standards.

Commenting on the results, MAFF says that they provide reassurance that dietary intakes of the elements studied are "not a cause for concern." However, it acknowledged that the survey was "not representative" of all industrial sites in the UK.

There are, indeed, a number of reasons to suspect that the study may not have identified the worst metal contamination hot spots around industrial sites.

Firstly, many of the industrial sites in the milk study, originally carried out for a dioxins survey, are unlikely to be major sources of the metals of most concern. Among them were five landfills, two power stations, two chemical works, a cement works, and four clinical and two chemical waste incinerators. Just two metals works were included, along with eight municipal incinerators which may have been significant metals sources.

Secondly, the vegetable sampling locations generally appear to have been too remote from the five metal works to pick up local fall-out. Only three of the 40 sampling locations were within two kilometres of the works. The average distance was over five kilometres, and three sites were ten kilometres or more away.

A recent study of the Baldovie municipal incinerator, closed down in 1996 after a controversy over its high emissions (ENDS Report 250, pp 12-13 ), suggests that even industrial processes whose main metal emissions come from tall stacks are unlikely to cause maximum contamination of land and crops at these distances. Both lead and cadmium levels in soils peaked at three kilometres downwind of the incinerator.2Other studies have suggested that low level "fugitive" sources make an important contribution to overall emissions from metal works. For instance, directional sampling surveys sponsored by the former Industrial Air Pollution Inspectorate in the 1980s showed that lead emissions from a variety of lead works enhanced local lead-in-air levels by up to ten times, with low-level sources such as material stockpiles and factory vents making a dominant contribution at some sites (ENDS Report 136, p 6). Metal fall-out from fugitive emissions occurs much closer to the source than from stack emissions.

Controls over fugitive emissions have since been tightened. Even so, recent monitoring has shown that fugitive sources are probably mainly responsible for elevated lead-in-air levels near a ferrous foundry and a lead-crystal glassworks in the West Midlands (see below), and it is crops grown near such processes which are likely to have the heaviest contamination.

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