Urban foraging: is it safe?

20th October 2021

[The featured photo presentes fruits of Italian hawthorn Crataegus azarolus collected in a city park in Split]

We associate foraging with the countryside, but in many parts of the world the countryside has become a place of intensive production in large monocultures sprayed with herbicides and pesticides. At the same time cities are growing in space, becoming large green spaces where food production is also taking place, e.g. in allotment gardens, roofs, balconies and individual gardens. City foraging is becoming trendy. Can we forage in cities? What are the rules? Is it safe?

When foraging in the city, we have to take into account a few dangers:

  1. Heavy metals
  2. Herbicides and pesticides
  3. Polycyclic aromatic hydrocarbons
  4. Parasite eggs

Ok, so let us start with heavy metals. They were of big concern a few decades ago, when petrol contained lead in the form of tetraethyllead. This chemical had an antiknock effect on the engine. However, it was discovered that lead has neurotoxic activity and most countries banned it by the early 2000s. Other heavy metals, e.g. cadmium, are also released by heavy industry or fertilizer applications. Still, heavy metals get through to the soil in smaller amounts in powder from tyres and brakes of cars. Yet other metals can be remnants of industrial or domestic waste. Heavy metals are heavy – it means they fly badly and usually remain close to the source of pollution, so mainly the soils in direct vicinity of roads are polluted. Moreover, different parts of plants will contain different amounts of heavy metals. The largest concentration will be in the roots, smaller in the leaves, and the smallest in fruits. The level of heavy metals in the soil is slowly decreasing as plants suck it up into leaves and branches, which are later removed somewhere else, so the concentration in the most polluted places is going down. Personally, I wouldn’t mind the occasional meal from city vegetables, provided they are not collected by busy roads. If we look at the results of the work of Galagher et al. (2021) we see that the content of lead recorded in wild foods in Boston was only slightly higher than in apples sold in shops and comparable with drinking tap water. Also the works of Stark et al. (2019) from Berkeley shows that the level of contamination for wild foods was within the norm. On the other hand, Unver et al. (2015) and Ugulu (2019) found significant amounts of heavy metals in a Turkish city, in the leaves of Urtica urens and Malva sylvestris respectively. The same team of Turkish researchers found that the fruits of walnuts (J. regia) collected in the city did not pose heavy metal risk, though the tree bark was much richer in them (Dogan et al. 2014).

Another concern at the moment is the use of herbicides, mainly glyphosate (Roundup and similar generic products). The streets of some countries are sprayed with them even a few times a year. I have seen an incredibly high frequency of use of these herbicides in the UK, for example. Places sprayed with herbicides several days before can be recognized by the gradual withering or yellowing of plants. Although occasional digestion of small amounts of such plants may not harm you, more frequent consumption can be detrimental to your long-term health. That is why it is dangerous to use plants growing near the pavement, where the herbicides are used the most.

Polycyclic aromatic hydrocarbons (PAHs) are present in the fumes from car exhaust pipes and from burning stoves, also emitted from asphalt. They can disturb your metabolism and be carcinogenic. As they are deposited on the surface of the leaves and fruits, make sure you wash them well, even if they are outside the reach of dogs. Plants with a rough, fluffy surface, such as the fruits of staghorn sumac Rhus typhina, will gradually ‘soak’ dust and chemicals from its surface like a sponge already a few days after the maturation of fruits. You should use these fruits in cities only directly after maturing. Bilek et al. (2017) found significant presence of lighter PAHs in birch sap collected in an agricultural area in Poland. Assuming that the PAH levels are higher in cities, the levels of these substances in city trees may be quite high.

Pavement plants are usually notoriously contaminated by dog faeces, and, a bit more rarely but commonly in poorer countries, even by human faeces. Excrement may contain whipworm eggs, which are notorious in many parts of the world but can fortunately be easily killed with pills. Canine faeces may also contain Echinococcus tapeworm eggs. Their larvae produce cysts in various organs. The cysts can grow, behaving like cancer, and not be detected for many years. That’s why it is of utmost importance to dip wild vegetables from the city into boiling water or boil them for a short while before consumption. The Chinese obsession of not using raw vegetables and stir-frying everything is actually a practical solution – a compromise between parasite egg extermination and preserving some nutrients killed by longer frying. To this day it is common in rural parts of Eastern Asia to fertilize gardens with human faeces.

On average, agricultural fields in the countryside probably have more pesticides than cities, but be aware that city garden fruit trees can be sprayed with them, and snail killing agents may be in use. Some cities also spray green surfaces with pyrethroids against mosquitoes, but these quickly break down.

Gallagher, C.L., Oettgen, H.L. and Brabander, D.J., 2020. Beyond community gardens: A participatory research study evaluating nutrient and lead profiles of urban harvested fruit. Elementa: Science of the Anthropocene, 8(1).

Stark, P.B., Miller, D., Carlson, T.J. and De Vasquez, K.R., 2019. Open-source food: Nutrition, toxicology, and availability of wild edible greens in the East Bay. PLoS One, 14(1), p.e0202450.

Unver, M.C., Ugulu, I., Durkan, N., Baslar, S. and Dogan, Y., 2015. Heavy Metal Contents of Malva sylvestris Sold as Edible Greens in the Local Markets of Izmir. Ekoloji Dergisi, 24(96).

Ugulu, I., Unver, M.C. and Dogan, Y., 2019. Potentially toxic metal accumulation and human health risk from consuming wild Urtica urens sold on the open markets of Izmir. Euro-mediterranean journal for environmental integration, 4(1), pp.1-11.

Dogan, Y., Unver, M.C., Ugulu, I., Calis, M. and Durkan, N., 2014. Heavy metal accumulation in the bark and leaves of Juglans regia planted in Artvin City, Turkey. Biotechnology & Biotechnological Equipment, 28(4), pp.643-649.

Bilek, M., Sadowska-Rociek, A., Stawarczyk, K., Stawarczyk, M. and Cieślik, E., 2017. Polycyclic aromatic hydrocarbons and pesticide residues in birch tree sap from an agricultural area. Medycyna Środowiskowa-Environmental Medicine, 20(1), pp.17-26.

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  • Minty 14th November 2021 at 5:40 pm

    Hi, very interesting and of course sad to know how many negative factors there are in urban foraging.
    However the post feels a bit incomplete, it would be nice to see some positive things about it.
    I’m not a scientist, but I try to consider more things. For me the biggest benefit of urban foraging is the fact that we add more diversity in our diet if we forage. What I mean by that is that if we only eat store bought or even homegrown vegetables, we are limited to those few species of plants that we come across over and over again. I believe that the diversity of food is one of the keys to a good health. So even though foraging in contaminated (of course depends on HOW MUCH contaminated) might bring us bad stuff into the bodies, it may also provide us with a wider variety of nutrients, minerals, vitamins, fibers, microorganisms that may strengthen our bodies and make them more durable or stronger to fight back that bad stuff. Does that make any sense?
    It’s just my theory that I’ve concluded over the years. It also makes me feel better about urban foraging. Without being able to gather plants around here, I’d be much more unhappy.

    Thank you!!