soil contamination

In early March The Age newspaper in Melbourne ran a story regarding soil contamination at a local environmental farm, CERES (Centre for Education and Research in Environmental Strategies). Having been active in the propagation area of the nursery I was shocked to read this. However CERES refuted the claims in a statement made shortly after. More information on this can be found at the CERES Safe Food page.


As a result of these concerns I started to think about the potential of soil contamination relating to my own attempts at urban agriculture. These concerns have been increased somewhat now that I am living in Richmond which was previously a highly industrial area. It was fortunate that an assignment for my course allowed me to use this topic for further research. Bellow is a short literature review conducted regarding the effects of soil contamination on urban agriculture. At some point I would like to investigate further this issue and will update this text. However this gives a brief overview of the general ins and outs of the issue.

Effects of contaminated soil in urban agriculture

 Increasing interest regarding the state of soil in the urban environment has prompted research into what potentially harmful substances may be present (Finster et al. 2003; Hazelton & Murphy 2010). More people living in cities are turning towards urban agriculture for their own food supply (Lander 2011) often growing in areas that pose a high risk of contamination (Craul & Lienhart 1999; Stilwell et al. 2008). The potential for contamination is greater in the city due to a mixed history of land usage (Finster et al 2003). The primary concern is the content of heavy metals; specifically lead (Stilwell 2008) as well as increased levels of other contaminants from other sources such as groundwater (Hinwood et al. 2005). The effects of contaminants pose a threat to plants, animals and humans through numerous transmission modes (Hazelton & Murphy 2010; Thornton et al. 2008). The primary concern to urban gardeners is the uptake of contaminates into the plants that are eaten and transferred into humans (Finster et al. 2003).  

Urban centres are unavoidably contaminated from a history of industrialisation. Residential properties show elevated levels of lead due to usage of lead based paints and proximity to road traffic. Despite a decrease in usage of lead for example, it still remains a common contaminant in soil (Stilwell et al. 2008). Many sites become contaminated from the usage of substances in situ or can be transferred through airborne particles or groundwater movement (Craul & Lienhart 1999; Hinwood et al 2005). Many sites for urban development and community gardens are on former industrial properties (Pless-Mulloli et al. 2004) and the condition of the soil is not always well tested for, depending on regulations in place at the time of building or standards for acceptable levels of contaminants (Hazelton & Murphy 2010; Stilwell et al. 2008; Thornton et al. 2008). Sites may also already have some level of contamination due to naturally high occurrences of lead, acid sulphite, salt or higher than usual levels of trace elements depending on geography (Finster et al. 2003; Hazelton & Murphy 2010). High usage of fertilisers and pesticides by gardeners can be another source of elevated levels of substances in soil (Hazelton & Murphy 2010). The presence of these elevated levels of undesired substances is a concern to urban farmers who often turn to home gardening to avoid consuming treated mass farmed produce (Lander 2011). However studies into how contaminants affect food crops, and thus humans or animals, indicate the risk is dependent on a number other factors (Finster et al. 2003; Hazelton & Murphy 2010). 

Irrespective of the source of contamination, research shows that increased levels of contamination may not be harmful (Thornton et al. 2008). Soil with a neutral pH level of 6.5-7.5 decreases the mobility of contaminants, making them ‘biologically inert, thus not presenting an obvious risk’ (Thornton et al. 2008, p.568). Soils with high acidity create the highest risk that can be further increased with the usage of contaminated water. Gardens watered with ground water with high levels of iron sulphide as observed by Hinwood et al. (2005) in their study showed higher levels of heavy metals in garden soil. The soil pH and its effects create varying risk for plants. Crops grown for consumption by animals or humans absorb differing amounts of contaminants into different parts of their structure. Plants with edible roots show the highest level of absorption followed by leafy shoots, and least amounts in fruits (Finster et al. 2008). Despite Finster et al. (2003) study, the acceptable levels of heavy metals and other elements vary across states and countries. Agricultural standards are cited as being the strictest for accessing contamination (Heinegg et al 2002). However organic certification requirements are ten times lower than of agricultural standard in Australia (Biological Farmers Australia 2010). These standards are important when looking at the relationship of contaminants and food, and what individuals see as a safe level for their garden. However Finster et al. (2003) cite (USEPA, 2001) an even higher acceptable level of lead in areas safe for child to play. There are observations children are at higher risk in urban areas through oral ingestion of soil that contain lead (Finster et al. 2008).  

To gain an accurate assessment of urban soil an in depth analysis is required to fully understand the land (Stilwell et al. 2008). Even within a single property the variation in levels of contamination can be significant and require different methods of treatment (Craul & Lienhart 1999; Heinegg et al. 2002). There is an ongoing risk that a site clear of contamination or one which has been remediated, is still susceptible to (re) contamination due to its proximity to sources of contamination. It is a continual process of testing and evaluation of soils to address imbalances as they occur (Hazelton & Murphy 2010). Contamination can also arise through various soil treatments. The transferal of waste material to other sites or chemical treatments used in situ is a potential cause of additional remediation work (Heinegg et al. 2002). In most instances it is recommended to use raised garden beds with fresh imported soil to avoid risk of consumption of contaminants through food plants (Finster et al. 2003; Heinegg et al. 2002; Johnson 2010; Stilwell et al. 2008). This is the most cost effective and accessible to gardeners. 

Urban farmers need to address the issue of contamination in the soil used to grow produce. It must be accepted that growing produce in the city has a level of inherent risk due to the high levels of contamination in air, water and soil. The level of risk of this is dependent on the history of the site in question and proximity to additional sources of contamination. Despite the additional risk, soil must be assessed closely to determine the exact levels of unwanted materials present and if they able to be transmitted through plants based on soil pH and solubility. Further care can be taken through careful planning of what crops are to be grown based on their ability to take up heavy metals and other elements and which parts of the plant are to be consumed. There is a very interesting discussion on what proves to be the most beneficial; growing produce locally to reduce food miles and having direct control over the food chain (Lander 2011) and what additional risk urban farmers face by not having a detailed understanding of what is in the land used. 

 Reference list:  

Biological Farmers Australia 2010, Australia Certified Organic Standard 2010 – version 1.0, Biological Farmers Australia Ltd., Australia, accessed 28 March 2012.  

Craul, P, & Lienhart, J 1999, Urban Soils : Applications And Practices / Phillip J. Craul, New York : Wiley, c1999.  

Finster, M, Gray, K, & Binns, H 2004, 'Lead levels of edibles grown in contaminated residential soils: a field survey',Science Of The Total Environment, 320, 2/3, pp. 245-257, Global Health, viewed 28 March 2012.  

Hazelton, P, & Murphy, B 2010, Understanding Soils In Urban Environments / Pam Hazelton And Brian Murphy, Collingwood, Vic. : CSIRO Publishing, 2011.  

Heinegg, A, Maragos, P, Mason, E, Rabinowicz, G, Walsh, H 2002, Soil contamination and urban agriculture; a practical guide to soil contamination issues for individuals and groups, Quebec, Canada, viewed 28 March 2012.  

Hinwood, A, Horwitz, P, Appleyard, S, Barton, C, & Wajrak, M 2006, 'Acid sulphate soil disturbance and metals in groundwater: implications for human exposure through home grown produce', Environmental Pollution (Barking, Essex: 1987), 143, 1, pp. 100-105, MEDLINE, viewed 28 March 2012.  

Johnson, Lorraine 2010, City Farmer : Adventures in Urban Food Growing, e-book, accessed 28 March 2012.  

Ladner, Peter 2011, The Urban Food Revolution : Changing the Way We Feed Cities, e-book, accessed 28 March 2012.  

Pless-Mulloli, T, Air, V, Vizard, C, Singleton, I, Rimmer, D, & Hartley, P 2004, 'The legacy of historic land-use in allotment gardens in industrial urban settings: Walker Road allotment in Newcastle upon Tyne, UK', Land Contamination & Reclamation, 12, 3, pp. 239-251, Global Health, viewed 28 March 2012.  

Stilwell, D, Rathier, T, Musante, C & Ranciato, J 2008, ‘Lead and Other Heavy Metals in Community Garden Soils in Connecticut’, The Connecticut Agricultural Experiment Station Bulletin’ vol. 1019, viewed 28 March 2012.  

Thornton, I, Farago, M, Thums, C, Parrish, R, McGill, R, Breward, N, Fortey, N, Simpson, P, Young, S, Tye, A, Crout, N, Hough, R, & Watt, J 2008, 'Urban geochemistry: research strategies to assist risk assessment and remediation of brownfield sites in urban areas', Environmental Geochemistry And Health, 30, 6, pp. 565-576, Global Health, viewed 28 March 2012.  

Tracey, David 2011, Urban Agriculture : Ideas and Designs for the New Food Revolution, e-book, accessed 28 March 2012.