Urban ecosystems are at risk from the rapid growth of population and poverty. City services become overstretched, local natural resources deteriorate and it is usually the poorest people whose health and safety are most compromised by these environmental problems.

However, cities are not only concentrations of demand but also nutrient sinks and repositories of other untapped natural resources. Nutrients are found in the vast quantities of wastewater and organic residues generated in urban areas. Cities also contain underutilized land and water surfaces that can be put to productive use.

Understanding both positive and negative health effects on households and the urban ecosystem is essential for determining strategies that multiply benefits and mitigate risks.

Household pesticide use in urban production of vegetables and flowers in Asia and Latin America carries serious risks. Heavy dependence on local suppliers for information and products often results in regular use of highly toxic pesticides not necessarily related to pest type or pest pressure. The geographical and temporal proximity of urban conditions and production chain linkages exacerbate risk, as when pesticides are prepared and used in places accessible to densely populated areas, or when heavy applications on jasmine flowers produce skin problems in garland makers and traders in the Philippines. Alternative Integrated Pest Management strategies are now being introduced, including through farmer field schools, to mitigate these negative feedbacks.

Urban households are also vulnerable to other contaminants. Farmers in cities like Kampala and Yaounde in Sub-Saharan Africa take advantage of the nutrients in city wetlands and inland valleys into which much of the city's liquid wastes drain. But they can also contain heavy metals and pathogens. Air pollution is another contaminant pathway for heavy metals being evaluated for risk. Levels of contamination and the point and non-point sources are being determined in different anchor sites for formulating mitigation actions, including policy recommendations.

On the positive side, urban household production contributes essential nutrients needed by poor producers' and consumers' families, such as indigenous leafy vegetables produced on a small scale around Yaounde. Produce such as vegetables, milk and eggs are consumed or sold depending on priorities for food and cash needs. In Latin America it was found that a major target for cash earnings are children's education costs.