Safety and urban-grown fruit

Some may be concerned about the safety of fruit grown in the city, considering the amount of air pollution in an urban environment. One of our volunteers, Jessica Langer, did some research on the safety of urban grown fruit. To learn more about her discovery, read on:

Note: before our orchard was planted, the soil in Ben Nobleman Park was tested by Parks, Forestry and Recreation and was concluded to be safe.

Research-based Safety Recommendations Regarding Fruit Grown In the Prospective Ben Nobleman Park Community Orchard

Jessica Langer, Ph.D.

Please keep in mind that this is a work of preliminary research and is a literature review; the recommendations made in this document are based on an overview of the related scientific literature rather than the results of any testing of the prospective site itself.

There is some concern about heavy metal concentrations in soil in general, which may affect both fertility of the soil and safety of the resulting produce. However, many of the chief ways in which soil is contaminated, such as irrigation with contaminated water and the presence of industrial runoff, do not apply in this instance. The grade of the land – the park is at the top of a hill – means that even if residents nearby use pesticides or other contaminants in their own gardens, the runoff is unlikely to affect the park.

Because there was an orchard on or near this site in the past, and because pesticide use was more widespread in those years and we did not have the same information about safety that we do now, there may be pesticide residues of heavy metal, such as lead and arsenic, in the soil; see Ernie Hood’s study of urban orchard properties in LA (2006). Copper sulfate was another pesticide in common use during the time the orchard was present. However, in Hood’s article, he emphasizes that these metals are not generally present in the fruit itself, citing soil scientist Frank Peryea’s recommendation that “there is little risk from eating plants grown in this type of soil, but… home gardeners [should] rinse off produce before bringing it into the home, then wash it again with a detergent and scrub brush to remove any remaining soil particles” (A472). Because fruit from trees is less likely than garden vegetables to have direct contact with soil, the risk of contamination by soil particles is somewhat lower. Even if there were heavy metal contamination in the soil itself, whether from airborne or pesticide residues, “heavy metal concentrations in tree fruits are very low even when grown on contaminated soils (Acta Horticulturae workgroup, 2001)”.

Much of the research done into urban and peri-urban agriculture in relation to food safety has been based in developing countries, such as China (i.e. Huang et al 2005), where environmental influences of concern are factories and other major, complex pollutant entities rather than four-lane highways. Therefore, although, for instance, there is an issue with cadmium contamination in orchard soil in Guangzhou, China, this is unlikely to be an issue in Ben Nobleman Park; the cadmium in the Chinese soil is likely to be a result of heavy industrial contamination, which is not a concern here.

Most of the concern regarding contamination in the Ben Nobleman Park orchard relates to airborne contaminants from the nearby motorways, rather than contaminants in the soil. K. Ruby Blume, an urban gardening expert in Oakland, believes that there is little to no additional risk in urban fruit from airborne pollutants. In a recent column, she writes: “Toxins from air pollution are unavoidable, but since we are breathing the air every day, eating fruits or vegetables exposed to the same amount as we are on a daily basis is going to be no worse.  There are no studies that show a significant build up in fruit from air pollution” (http://www.theoakbook.com/MoreDetail.aspx?Aid=3007&CatId=15).

RECOMMENDATIONS

Although the particular contamination concerns at Ben Nobleman are likely low-risk for the fruit produced by the prospective orchard, and are likely to be in the superficial category rather than in the flesh of the fruit, I would recommend testing the soil before commencing planting, or at least before recommending that people eat the fruit. This will also help guide the coordinators as to which varieties of tree to plant. However, the evidence points to several conclusions:

1.     The safety of the fruit in the Ben Nobleman Park orchard is likely not significantly lower than the safety of the fruit grown anywhere in a similarly urban part of Toronto; the airborne contaminants from the roadway can be washed off.

2.     The concern about the location is mostly from airborne contamination, and airborne contaminants are unlikely to collect in the soil in any significant amount; therefore, there is little to no risk from eating the washed fruit.

3.     Even if the soil in the park was found to have a higher-than-average concentration of heavy metal contamination, the fruit borne by the orchard trees would be unlikely to harbour dangerous, or even elevated, levels of these contaminants. Any concern would be for the fertility of the soil rather than the safety of fruit grown in it.

REFERENCES

Acta Horticulturae Workgroup. “Heavy Metal Contamination in Deciduous Tree Fruit Orchards: Implications for Mineral Nutrient Management.” ISHS Acta Horticulturae 564: IV International Symposium on Mineral Nutrition of Deciduous Fruit Crops (2001). Available only on CD-ROM or at http://www.actahort.org/books/564/.

Blume, K. Ruby. “Are City Fruit Trees Safe?” Oakbook 15 April 2009. Accessed 19 April 2009 at http://www.theoakbook.com/MoreDetail.aspx?Aid=3007&CatId=15.

Hood, Ernie. “The Apple Bites Back: Claiming Old Orchards for Residential Development.” Environmental Health Perspective 114, Issue 8 (August 2006), pp. A470–A476.

Huang Biao; Shi Xuezheng; Yu Dongsheng; Öborn, Ingrid; Blombäck, Karin ; Pagella, Timothy F.; Wang Hongjie; Sun Weixia; Sinclair, Fergus L.  (2005). “Environmental assessment of small-scale vegetable farming systems in peri-urban areas of the Yangtze River Delta Region, China.” Agriculture, Ecosystems & Environment 112, Issue 4 (March 2006), pp. 391-402.

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