Human Stresses On the Environment-Metal Contamination in topsoils

April 6, 2011

The environment is steadily changing in the world around us. It is constantly being affected by everything humans do on the planet as far as waste disposal, pollution, and the cutting down of trees. The two most important factors in environmental change is the metal contamination in urban soils. Two case studies that best show these instincts take place in the overcrowded country of China.
Hong Kong is one of the most densely populated cities in the world with a population of over 6.8 million and an area of only 1067 km squared(Li p.1361) so I’ll draw your focus there. Due to Hong Kong’s rapid growth rate and urbanization all of its parks and recreational areas are built close to major roads or industrial areas. The placement of these parks leads to what is known as heavy metal contamination in urban soil. According to the Environmental Engineering Unit and the Department of Civil and Structural Engineering, “atmospheric pollution is one of the major sources of heavy metal contamination(USDA p.1).” Heavy metals can accumulate in topsoil from atmospheric deposition by sedimentation, impaction and interception. Top soils and roadside dusts in urban areas are indicators of heavy metal contamination from atmospheric deposition(Li p. 1361). The United States Department of Agriculture says the main causes of this sort of contamination include; “mining, manufacturing, and the use of synthetic products (e.g. pesticides, paints, batteries, industrial waste, and land application of industrial or domestic sludge).” According to the USDA and the NCRS the most common problem causing cationic metals (metallic elements whose forms in soil are positively charged cat ions e.g., Pb2+) are mercury, cadmium, lead, nickel, copper, zinc, chromium, and manganese. The most common anionic compounds (elements whose forms in soil are combined with oxygen and are negatively charged e.g., MoO42-) are arsenic, molybdenum, selenium, and boron(USDA p.1).
Knowing that the placement of these parks is potentially hazardous a soil survey was conducted in Hong Kong’s urban parks. Soil samples and street dusts were taken from over 60 parks and public amenity areas in old urban districts, industrial areas and New Towns of the territory. Soils were also sampled in the remote country parks to establish the baseline conditions. The conclusion was that the urban soils in Hong Kong had elevated concentrations of metals. Soils from 65 parks in Hong Kong were tested in the study to show the different land use and traffic conditions. Out of all the 65 parks, 21 of them were on the Hong Kong Island, 22 of them were in the Kowloon Peninsula, and the 22 left were in the New Territories. These urban parks can be split into three groups; residential, commercial, and industrial areas. Street dust samples were also taken around chosen parks during the sampling. Collectively there were 505 soil samples and 45 roadside dust samples gathered. To make sure that the general baseline was obtained approximately 300 soil samples were also taken from 15 country parks in the study(Li p.1362).
The studies concluded that soils in urban parks in Hong Kong have elevated concentrations of various amounts of heavy metals in them. The mass amount of these in top soils are more obvious in the urban parks rather than that of the country parks, meaning that this is due to the location of the parks and is coming from the traffic sources, especially the vehicle tyres. A solution to this problem is still yet to be seen but should be looked at as the contamination of the soil could be potentially hazardous to humans even though it stemmed from them.

Heavy Metal Contamination and street dusts in Hong Kong. Applied Geochemistry, Volume 16, Issues 11-12, August-September 2001, Pages 1361-1368 Xiangdong Li, Chi-sun Poon, Pui Sum Liu

Particular air pollution in urban areas of Shanghai, China: health based economic assessment. Science of The Total Environment, Volume 322, Issues 1-3, 25 April 2004, Pages 71-79. Haidong Kan, Bingheng Chen

Heavy Metal Soil Contamination. Soil Quality-Urban Technical Note, No.3. September, 2007. United States Department of Agriculture. Natural Resources Conservation Service. Pg.1-7.