This discussion paper is prepared by Henk de Zeeuw, Co-ordinator of the Resource Centre on Urban Agriculture and Forestry (RUAF), ETC, the Netherlands; and Karen Lock, Visiting research fellow, London School of Hygiene and Tropical Medicine, UK.
This working group will deal with the health and environmental aspects of urban and periurban agriculture (UPA). UPA can have both negative and positive effects on the health and environmental conditions of the urban population. The positive aspects include a/o. reduction of urban food insecurity, improved access to food and improved diets of the urban poor, better physical and psychological health of the population due to greater physical activity, outdoor relaxation and ameliorated sanitation and greening of the direct living environment.
We invite participants in this workshop to report and discuss both positive and negative impacts of UPA on health and the environment, although most of the above-mentioned positive impacts on health will be dealt with more extensively in the workshop on ‘UPA, nutrition and food security’’. However, tThe working group on UPA, health and environment –- and thus also this paper - will mainly focus on the health risks of UPA and seek to formulate effective policies at city and national levels, that prevent or mitigate such risks.
Urban agriculture can be defined as the growing of plants and the raising of animals for food and other uses within urban areas (intra-urban agriculture) and in the fringe of urban areas (periurban agriculture), and the processing and marketing of the resultant products. UPA systems include root crops, vegetables, aromatic and medicinal herbs, fruit crops, and livestock of all shapes and sizes. A smaller number deals with other plants, such as ornamentals and tree seedlings. Within food crops, the more perishable and relatively high-valued vegetable and animal products and by-products are better represented. Food and non-food production is often mutually complementary, often along gender lines, they reinforce not only food security but also income benefits, at individual and household levels. Urban farmers are mainly small-scale family enterprises, but also medium sized and larger enterprises are encountered. Urban agriculture (especially and more so intra-urban agriculture) is often done in addition to other employment.
Like rural agriculture, UPA entails risks to health and the environment, if not managed and carried out properly. It is essential to address the health risks associated with urban agriculture for two main reasons (Flynn 1999):
City authorities have often been reluctant to accept urban agriculture because of perceived health risks. Nevertheless, in most cities in developing countries (as well as in many countries in transition in Eastern Europe), urban agriculture is practised to a substantial scale, despite prohibitive laws and regulations. Hence, rather than general laws prohibiting urban agriculture, which are largely ineffective, policies are needed that actively manage the health risks related to urban agriculture.
To formulate urban agricultural policies that improve the health of the urban population, it is important to critically examine the evidence for both health risks and benefits. We need to look at how the risks of urban agriculture can be minimised and the benefits increased. In order to be able to do so, we must specify the environmental conditions under which UPA-related health problems occur (i.e., type of agriculture, farm management practices, characteristics of the location, etc.) and the groups that are most vulnerable to those impacts, and the factors that determine this vulnerability (e.g. poverty, gender, age, main occupation). We must also discuss what factors currently restrict the urban poor from engaging in safer agricultural and food practices, as well as the capacity of city authorities to implement certain policy measures and to calculate their cost-effectiveness.
The main health risks associated with UPA can be grouped into the following categories:
Although there is no directly comparable information about the global burden of disease for each of these categories of health risks, we have presented them The health risks are presented above in a sequence corresponding with our estimate of their impact importance on for human health (from highest to lowest risk). , This whichis open for debate.
A review of the available literature indicates that, although insight into the potential health risks of urban and periurban agriculture is growing, detailed information on the actual health impacts of UPA is scant. Many of the health risks are not specific to UPA, and much of the following discussion is taken from the wider agricultural literature. Further specification for urban conditions is urgently required.
The main use of solid waste is as a soil improver (household wastes, market refuse, sewerage, night soil, manure, fish wastes, and agro-industrial wastes). Agro-industrial wastes, household refuse and market wastes are also used to produce feed for livestock and fish.
Composting is the most common form of processing urban organic wastes. Composting reduces several health risks by:
There are four main health risks related to the re-use of organic wastes:
Liquid waste from domestic sewage is widely used for irrigation and fertilisation of field crops, perennials and trees, biogas production, and fish ponds. A large part of the wastewater used is untreated or poorly treated.
Wastewater contains various bacteria, protozoan parasites, enteric viruses and helminths. These risks are not limited to official wastewater but often also apply to rivers and other open water sources, as indicated by figures gathered by Westcott (FAO, unpublished, cited in Birley and Lock, 20001999): 45% of 110 rivers tested carried faecal coliforms levels higher than the WHO standard for unrestricted irrigation.
There are many forms through which untreated wastewater can lead to human diseases in UPA. Coliform bacteria are mainly transmitted to humans from wastewater via the contamination of crops irrigated with wastewater. Another route is by consumption of contaminated meat from domestic animals that ingested tapeworm eggs from faeces in untreated sewage. Poorly treated sewage may contain viable stages of the hookworms that live in moistened soils and affect agricultural workers who expose their bare skin to the soil. Transmission of pathogens may also take place by fertilisation of fish ponds with human and animal wastes (e.g. overhanging latrines, overhanging poultry cages, ducks, addition of urban night soil and use of wastewater).
Furedy (1996) points out that official attitudes towards the health risks associated with re-use of urban wastes have historically changed with necessity. Furthermore, she believes that perceived health risks of the re-use of urban wastes in agriculture are overstated and that regulations of waste re-use are frequently outdated or lack comprehensiveness.
Armar-Klemesu et al. (1998) indicate that the major sources of bacterial contamination of fresh vegetables may draw from the distribution, handling and marketing system rather than from production.
Prevention and control measures suggested in the literature:
The workshop participants are invited to discuss the cost-effectiveness and applicability of these suggestions and to propose other measures.
Malaria occurs in many environments but particularly in areas where irrigation is practised. Adaptation of malaria mosquitoes to urban environments has been observed worldwide. However, most malaria is found on the periphery of the cities where mosquitoes breed in ricefields, riverbanks and garden wells. The malarial mosquito breeds mainly in relatively clean water.
Filariasis is transmitted by the mosquito, Culex quienquefasciatus, which breeds in standing water which is highly polluted with organic matter. This is typical of dense human settlements (e.g. pit latrines, blocked sewage drains, cesspits and septic tanks, soak pits and poorly designed sewage-treatment plants. Filariasis is spreading rapidly due to urbanisation.
The Aedes mosquito, which is the main vector of dengue, breeds in water containers that include much solid waste (e.g. tin cans, coconut husks, rubber tyres, water storage jars).
Chagas disease has recently been emerging in periurban areas mainly in Latin America.
Poor disposal of organic solid waste (animal manure, crop residues and other farm refuse) may also attract rodents and flies that may be carriers of diseases (e.g. plague), and scavenging by domestic animals (e.g. cats, pigs and rats) is associated with a range of food-borne diseases such as amoebic and bacillary dysentery
Suggested prevention and control measures (please comment):
Urban agriculture provides various potential exposure pathways to agrochemicals including occupational and environmental exposure and consumption. The intensive use of agrochemicals (fertilisers, pesticides, fungicides) may lead to residues of agrochemicals in crops or groundwater, and negative effects on the health of agricultural workers. Because of differences in usage, the level of risk of crop or groundwater pollution due to agrochemicals is higher in intensive commercial horticulture, especially for vegetables, than in traditional and subsistence farming (WHO Commission on Health and Environment 1992).
Acute poisoning due to agrochemicals can cause a range of symptoms which are often not correctly diagnosed (e.g. dizziness, diarrhoea, headache, memory impairment, convulsions, coma, liver and kidney impairment and lung fibrosis). Agrochemicals are also a major source of suicide worldwide.
Chronic illnesses have been associated to residues in foodstuffs due to concentration of agrochemicals in the food chain, including vegetables, red meat, poultry and eggs, and residues can be found in human milk (FAO and WHO 1988).
Suggested prevention and control measures include:
Please share with us your experiences with the proposed measures and available alternatives.
The main causes of soil pollution from heavy metals (including lead, cadmium, chromium, zinc, copper, nickel, mercury, manganese, selenium, mercury and arsenic) are irrigation with water from streams and wastewater contaminated by industry, the application of contaminated solid wastes and the use of former industrial land contaminated by spilled oil and industrial wastes.
Important sources of heavy metals are smelters, refineries, manufacturing plants, vehicles, metalliferous mines, ceramic industry (lead and cadmium), leather tanneries (chromium salts), lignite-based power plants, aluminium industry, electronics industry, and metallurgical industry. Some heavy metals precipitate in sewage sludge, which can therefore contain rather high concentrations.
The heavy metals may accumulate in the edible parts of crops that are consumed by people or fed to animals. Plant uptake of heavy metals varies, which opens the possibility to adapt the choice of crops in relation to the degree and type of contamination. Generally, the highest amounts of heavy metals accumulate in the leaves, whereas the lowest contents are located in seeds. Beans, peas, melons, tomatoes and peppers show very low uptake figures. Plant uptake of heavy metals (especially of cadmium and lead) also varies with soil pH (Iretskaya and Chien, 1999).
Though heavy metal content in soils of most cities in developing countries are so high as to be able to cause acutely toxic symptoms, their increased concentration in the human food chain over a long period can provoke detectable damage to health (carcinogenic and mutagenic effects).
Puschenreiter et al. (1999) conclude that, after considering the several available pathways to reduce the transfer of heavy metals to the human food chain, urban soils with slight heavy metal contamination can be used safely for gardening and agriculture if proper precautions are followed. However, Birley and Lock (2000) argue that little is known of the chronic health effects of consuming tiny amounts of heavy metals over long periods of time, and that further research is needed.
Suggested prevention and control measures encountered in the literature, include the following (please qualify and/or add alternative measures):
Zoonotic diseases are infectious diseases transmitted through direct contact of human beings with animals during production processes or ingestion of contaminated animal products.
Two major bacterial diseases carried by cattle are bovine tuberculosis and brucellosis. Bovine tuberculosis is transmitted via the ingestion of contaminated unpasteurised milk from infected cows, and causes symptoms similar to respiratory tuberculosis. Bovine tuberculosis is transmitted via the ingestion of contaminated unpasteurised dairy products or through direct contact with infected animal material (blood, urine) and forms a main occupational hazard of livestock farmers and slaughterhouse workers. It can also spread by air-borne transmission and inhalation (e.g. in the neighbourhood surrounding a slaughterhouse).
Taeniasis and cysticercosis (beef and pig tapeworm) are transmitted by consumption of meat infected with tapeworm eggs congested by animals that scavenge on human faeces, or of crops irrigated with improperly treated sewage. Pig tapeworms create more severe effects in humans than beef tapeworm. Trichinosis is transmitted by consumption of infected meat of pigs that scavenge on food waste and dead animals.
Anthrax is most common in people who work with livestock or work in animal product industries (e.g. tannery). It can be transmitted through a cut in the skin, by inhalation of bacterial spores or consumption of infected meat.
Leptospirosis (Weil’s disease) is transmitted through the contact of humans with infected animal urine or contaminated feedstuff or by swimming in or drinking from water supplies contaminated with animal urine.
Salmonella and campylobacter are can be transmitted through contamination of animal feed. Animals (especially poultry) shed pathogens in their faeces in slaughterhouses, which may infect the meat. The wastewater discharge from intensive poultry farms can carry heavy loads of these micro-organisms and may contaminate drinking water supplies.
Suggested preventive and control measures include:
As was explained in the conference announcement, we will have three rounds of discussion. For each of these, we have formulated some leading questions. But Participants should also feel free to put forward other questions that they feel should be discussed. Next to your contributions to each round's discussions, we also welcome case studies, ‘best practices’, thematic papers and videos, which will be published on the information market (in the Urban Health section)
First session: Fact finding and situation analysis
Second session: assessment of alternative policy measures
Third session: from planning to action
Armar-Klemesu M, Akpedonu P, Egbi G & Maxwell D. 1998. Food Contamination in urban Agriculture: Vegetable production using waste water. In: Armar-Klemesu M. and Maxwell D. (eds), Urban Agriculture in the Greater Accra metropolitan Area, Report to IDRC, (NMIMR, Legon).
Birley, M.H. and Lock, K. The health impacts of peri-urban natural resource development.
University of Liverpool Press, 2000
(the paper may be more accesible to people)Birley MH and Lock K. 1999. Health and peri-urban natural resource production.
Environment and Urbanisation, 10(1): 89-106.
FAO & WHO. 1998. Guidelines for predicting the dietary intake of pesticide residues. Bulletin
of the World Health Organisation, 66: 429-434.
Flynn Kathleen. 1999. An overview of public health and urban agriculture: water, soil and crop contamination & emerging zoonosis. IDRC - Cities Feeding People Report 30.
Furedy Christine. 1996. Title of paper? Solid Waste Reuse and Urban Agriculture – dilemmas in developing
countries; the bad news and the good news. Joint international Congress of the
Collegiate Schools of Planning and Association of European Schools of
Planning, Ryerson Polytechnic University, Toronto.
Iretskaya SN & Chien SH. 1998. Comparison of cadmium uptake by five different food
grain crops grown on three soils of varying pH. Comm. Soil Sci. Plant Anal. 30: 441–448.
Puschenreiter Markus, Hartl Wilfried & Horak Othmar. 1999. Urban agriculture on heavy metal contaminated soils in Eastern Europe. Vienna: Ludwig Boltzmann Institute for Organic Agriculture and Applied Ecology.
WHO Commission on Health and Environment. 1992. Report of the panel on food and agriculture. Geneva: WHO.