Summary, Miljøstyrelsen

Optagelse af metaller og PAH-forbindelser i grøntsager og frugt

Summary

Studies of fruits and vegetables

In literature, a number of studies of the uptake and transport of metals and xenobiotics in plants are described. Most of these studies are based on experiments, in which the soil was spiked with the substances immediately before test start, and the results show a potential for bioaccumulation in plants of several substances. In contaminated soil, the origin of the substances varies greatly just as they may have aged in the soil for a number of years, which reduces the bioavailability of the substances, and only few investigations of the uptake under such conditions are available.

In 1999, in connection with the revision of the Danish EPA "Guidance Document regarding advisory to the residents on slightly contaminated soil", the Soil Contamination Department of the Danish EPA initiated field surveys in collaboration with the Agency of Environmental Protection - City of Copenhagen and the County of Northern Jutland.

The objective of the surveys was to assess the importance of the content of PAH compounds and metals in crops grown in contaminated soil under realistic conditions - especially in relation to the concentrations of soil contamination that are relevant with regard to the advisory interval. The advisory interval is limited by a soil quality standard (under which the use of the soil is without restrictions) and a cut-off value (above which any contact with the soil should be avoided). The surveys included field experiments with vegetables and collection of fruits, berries and nuts from existing trees and bushes from non-contaminated soil as well as from soils with various degrees of contamination. Samples of root crops (i.e. potatoes and carrots) were analysed with as well as without peal.

In general, the investigations showed that when the contamination of the soil increased, the content of most of the contaminants in the vegetables increased as well, while such a correlation could not be demonstrated for fruits and berries. With regard to the PAH compounds, however, the results showed a potential tendency towards higher concentrations in berries grown in heavily contaminated soils than in berries grown in non-contaminated soils.

The conclusion of the surveys was that the substances investigated were only taken up through the roots and transported to other parts of the plants to a very limited extent but that, on the contrary, the substances were taken up in those parts of the plants that are in direct contact with the soil, which primarily applies to root crops. Furthermore, uptake in the above-soil parts may occur from soil deposited on the plants from soil splashes at heavy rainfalls or from whirled-up dust during dry periods. The investigations showed that the substances were found in the highest concentrations in root crops, i.e. potatoes and carrots, but that far the greater part may be removed by peeling.

As the concentration of the substances in the crops is far below the concentration in the soil, the surveys attached great importance to avoiding any traces of soil in the samples for analysis - partly by thorough washing and partly by avoiding berries with soil splashes. The conclusion is based on the assumption that no soil is ingested together with the crops.

Health assessments

Estimation of the contribution via food

The potential importance of the use of crops grown in contaminated soil in the everyday fare has been estimated. The estimations of the ingestion of heavy metals and PAH compounds have been made by use of a diet model developed by the Danish Veterinary and Food Administration.

As regards the metals, the estimated ingestion thus applies to the total fare, including crops (fruits as well as vegetables) grown in contaminated soil. The ingestion with the food, in which crops from contaminated soil are included, was compared with the ingestion with the food, in which only marketed crops are included (based on data from the Monitoring System of the Danish Veterinary and Food Administration).

As regards the PAH compounds, the estimations were made for benzo(a)pyrene as most data on concentrations in crops are available in literature for this compound and as the content of benzo(a)pyrene is often used in connection with risk assessment of PAH mixtures. As regards benzo(a)pyrene, results from vegetables grown in non-contaminated soil compared with results from contaminated soil were used for the diet model estimations. The concentrations found in fruits and berries were compared with literature data on the background level.

Health assessments

In connection with the ingestion of contaminated crops, children must be considered the most exposed group as they ingest proportionately larger amounts of food than adults.

Estimations show that when children by ingestion of marketed crops in average receive a contribution corresponding to 20% of the PTWI value, the contribution by ingestion of crops grown at the cut-off value corresponds to 25% of the PTWI when the potatoes are peeled - consequently an excess intake of lead of 5% of the PTWI value. When using potatoes with peel, the lead intake is considerable higher (47% of the PTWI).

As regards benzo(a)pyrene, an average excess intake by children of benzo(a)pyrene of approx. 5 ng/day was estimated by consumption of vegetables (including peeled root crops) from contaminated soil. The excess intake corresponds to approx. a fourth of what is acceptable in relation to intake of soil just meeting the soil quality standard. A separate assessment of benzo(a)pyrene was elaborated regarding benzo(a)pyrene in fruits and berries. The results of this part of the survey were compared with a literature-based background level of 0.02-0.04 痢 benzo(a)pyrene/kg wet weight in fruits and berries.

In general, the above estimations are considered very conservative as they overestimate considerably the excess intake. First, the estimations are made on the basis of the upper limit of the advisory interval (as regards benzo(a)pyrene even with twice the cut-off value) and second, it must be expected that eventually the actual excess intake will be considerably lower than estimated as, generally, home-grown crops cannot cover the consumption all the year round.

On this basis, the supplementary contribution of contaminants as a result of the ingestion of crops grown in slightly contaminated soil is estimated to be moderate when the root crops are peeled.

Conclusions

In the crops, levels of PAH compounds (represented by benzo(a)pyrene) and lead, which are unacceptable with regard to health, can be found. This is due to the relatively high concentrations found in root crops in consequence of their direct contact with the contaminated soil. The major part of the content is found in the outer part of the root crops and may thus be eliminated by peeling. Even though peeling removes the major part of the contaminants, ingestion may result in an increased intake of PAH compounds (benzo(a)pyrene) and lead even if the excess intake from crops from slightly contaminated soil is moderate.

The extent of the excess intake is estimated on the assumption that all crops are thoroughly washed and that root crops are peeled. Strawberries were not included in the surveys but as strawberries are in relatively close contact with the soil and as they are difficult to wash thoroughly, it must (until further investigations have been made) be recommended that they are not eaten.

In principle, the excess intake of PAH compounds and lead is not acceptable as there are no lower limit to the harmful effects of these substances.

On the basis of an overall view including the nutritional benefits of the ingestion of fruits and vegetables, the Danish EPA finds, however, that the intake of home-grown crops should not be dissuaded as only moderate excess intake is in question but that some precautions should be recommended (washing and peeling).

However, when assessing whether growing of crops in slightly contaminated soil is acceptable, the assessment cannot be limited to the actual intake of crops. When growing vegetables, it is not practically possible to avoid uncovered soil and a subsequent exposure of humans (especially children) to soil and soil dust. Via this exposure route, an unacceptably high exposure of children to contaminants in the soil may occur. As growing of fruits and berries may take place without any occurrence of uncovered soil, the above reflection regarding whether the actual growing is problematic does thus not apply to fruits and berries.

In the actually investigated soil contaminations with respect to fruits and berries (allotments in Copenhagen and tar-contaminated sites in the Skaw) in which the cut-off values are generally exceeded, the Danish EPA finds on the basis of the test results that there is no reason for a dissuasion of the ingestion of fruits provided that they are thoroughly washed beforehand. Regarding berries, it is assessed that the ingestion of berries that are growing close to the soil surface or that when picked are dirty from soil must be dissuaded. The Danish EPA finds that there is no reason for further dissuasion of consumption of berries provided that they are washed thoroughly beforehand.