Lead and Cadmium in Soils 1991
Lead and cadmium soil contamination in Berlin varies considerably, particularly in allotment garden, agricultural, sewage farms, and forests. The number and distribution of measuring points for these areas give representative values. Other areas were tested with a much lesser test density. These surveys give only an initial overview of contamination degrees and distribution.
Allotment Gardens and Yards
The topsoil of allotment gardens everywhere is considerably contaminated with lead and cadmium. Both the 50th percentile value as well as the average value exceed greatly natural soil values – and that in areas where heavy metals can be absorbed by food crops. This was demonstrated by the Berlin Heavy Metal Measurement Survey analysis of food crops (see 01.03.3). In some cases, both elements were present at such levels that health risks incurred by direct contact with soil could not be ruled out.
Contaminated allotment gardens are found in all parts of the city, most heavily in the inner city. Lead levels show a more clear gradient than cadmium levels. There are considerable contamination level differences within a single area of gardens, sometimes even within a single garden.
The measurement values of differentiated follow-up tests of 1,600 allotment gardens conducted in 1989 and 1990 are not depicted in the map for graphic reasons. The values found at these sites are given in Table 3.
House yards are less contaminated. Levels exceeding index values were determined at few locations.
Agriculture and Horticulture
The majority of tested agricultural areas are considered only slightly contaminated. More than 50% of tested areas show levels within natural ranges for lead and cadmium. There is a clear regional differentiation of contamination. Cadmium levels exceeding applicable index values were found almost only in sites around the Gatow sewage farms. Lead levels are high here too, although few locations exceeded the index values. Soil contamination correlated with contamination of food and feed crops, also unusually high here (compare 01.03.3).
High heavy metal levels were also found in green spaces in northwest Berlin and in Lübars, due to larger amounts of humus and its greater capability for binding heavy metals.
Horticultural businesses did not exceed soil index values. Determined lead and cadmium levels were in the range of natural levels.
Particularly high cadmium contamination was found in almost all soils of former or still functioning sewage farms in Berlin and its vicinity (compare 01.10). The sewage farms in southern Berlin are more heavily contaminated than those in Gatow or northeast Berlin. There are great pollution gradations within single sewage farms. Soil contamination in the great majority of former sewage field areas, mainly used today for agricultural purposes, lead to the expectation of disturbing cadmium levels in the crops cultivated here. Contamination in crops cultivated on sewage farms have been determined. (cf. 03.03.3, Grün et al. 1990).
Lead is also accumulated in higher concentrations in sewage field soils, but concentrations remain under applicable index values. The homogeneous pollution levels determined in the test areas indicate that untested areas will have comparable heavy metal concentrations.
Forests and Green Spaces
High lead and cadmium levels were found in almost all forest topsoils. These values were, as a rule, under those found in areas for heavier anthropogenic (human) use (cf. Table 3). Heavy metal concentrations in organic horizon (not depicted) are usually higher than in mineral topsoil.
Contamination in depicted green spaces and other uses cannot be interpreted in context because of their wide heterogeneity. The inner city again shows higher contamination. Contamination levels in Schöneweide document the range of variation possible in inner-city areas.
Some playgrounds are contaminated with heavy metals. Some contamination levels were so high that health risks caused by direct contact with the soil cannot be ruled out.
Causes of Pollution
Causes of lead and cadmium soil contamination are mostly additives of contaminated materials (building rubble, cinders) some of which come from refuse dumps or industrial sites.
Such land fill is especially practiced in allotment gardens and house yards, green spaces and miscellaneous use areas. 115 allotment garden areas in West Berlin are on old deposit sites, old industrial sites, or suspected old contaminated sites. Conspicuous are large areas on the edge of West Berlin used today for allotment gardens (SenStadtUm 1991c). In the inner city there are large deposits of debris.
The highest heavy metal values are regularly found at these locations and are usually due to anthropogenic deposits. Significant contamination also appears in small areas, often from building activity or land-fill in gardens.
Considerable heavy metal deposits are also found in allotment gardens, house yards and green areas because of the use of contaminated compost and soil conditioners, especially from regular and long-term use. Contaminated composts at many locations were confirmed by the Berlin Heavy Metal Program. This is primarily caused by the composting of polluted waste (i.e., ash). The previously widely practiced use of contaminated sewage sludge compost (fertilizer) in allotment gardens, house yards and green spaces (used today only in small areas) contributed to soil contamination. Sewage farm sludge was used as soil conditioner for agricultural areas around the Gatow sewage farms.
Soil contamination in current and former sewage farms is due to contaminants in their waste waters. The contaminant spectrum of waste water is reflected in the soil. Variations in pollutant level between different sewage farms and within individual sewage farms are due to the length and intensity of waste water flow and origin. It is assumed that pollutants in waste water and treatment intensity were previously significantly higher than at sewage farms in use today.
Variations of pollution within individual sewage farms are due to non-homogeneous use. Soil contamination decreases with the distance from the waste water discharge pipes. Especially high values are regularly found in sludge drying areas and sedimentation basins. These relationships are clearly seen in comparing contamination levels in the 01.10 Map of Use of Sewage farms.
The lead and cadmium contamination around the Tiefwerder meadows exemplifies the effects of periodic flooding by contaminated surface waters.
Contamination of playgrounds is due to the use of contaminated surfacing and building materials, such as cinders and building rubble.
Inputs from the Air
Airborne heavy metals also contaminate the soil. This influence is more clear for lead than cadmium because of the much greater amounts of lead. Soil in the inner city is more contaminated than soil at the edge of the city. The highest contamination is found in the vicinity of commercial emitters, but also directly next to heavily-traveled streets (see 01.03.3).
Forest contamination is almost entirely due to airborne pollutants. Pollutant sources cannot be clearly determined in gardens and agricultural areas, because of regular supplements of soil conditioners and other substances to the topsoil.
The diversity of pollution and causes of contamination make it clear that the depicted lead and cadmium levels in topsoils at many locations illustrate only part of the entire contamination present. Many sites show contamination of other heavy metals, such as zinc, copper and chrome. The risk potential of soil is clearly higher at these sites. Sewage farms and old contaminated sites often had organic pollutants in relevant concentrations. It can be assumed that pollutants have been carried or washed into deeper soil levels at landfill sites, sewage farms, and sites where topsoils have low binding capacities.
It can also be assumed that comparable contaminant levels are present at the many sites not yet tested, particularly in East Berlin.
The Berlin Department of Urban Development and Environmental Protection is preparing possible action plans for reducing risks arising from soil contamination (see Table 2). But these can only be sensibly conceived after a thorough investigation of the causes of specific site contamination, and in consideration of the total spectrum of pollution. Additional information about soil characteristics is needed in some cases. This information would be given to users of those areas. Concrete safety or restoration measures have been initiated for particularly highly-contaminated playgrounds.