Risk assessment of sewage sludge used as fertiliser and soil conditioner in Norway


Report no: 2009: 30

Published: 21.08.2009

Main message:

The Norwegian Scientific Committee for Food Safety (VKM) has assessed the risk of using sewage sludge as fertiliser and soil conditioner. VKM concludes that consumption of food grown in soil with added sewage sludge does not constitute any significant health risk caused by the contaminants assessed.

It is, however, possible, that humans who only eat vegetables grown in soil with added sewage sludge may consume more cadmium and copper than the estimated tolerable intake levels, but the likelihood of this scenario is not assessed in this risk assessment.

Note that it is not allowed, according to the Norwegian legislation, to grow vegetables, berries or potatoes the first three years after adding sewage sludge.

The model used to calculate soil concentrations does indicate a potential increase in the soil concentration of the inherent toxic metals Cd and Hg as well as Cu and Zn.

It is therefore recommended that the concentrations of these metals in sewage sludge used for agricultural purposes should be monitored. Furthermore, continued efforts to reduce the content of these metals in sludge are encouraged.

VKM considers the use of sewage sludge to constitute low risk for the soil ecosystem. Octylphenols, nonylphenols and linear alkylbenzenesulfonate (LAS) were the only contaminants that are estimated to reach soil concentrations exceeding the PNEC (predicted no-effect concentration) in agricultural soils.

However, these are rapidly degradable substances (t1/2 in soil = 8-10 days) where the highest concentrations were found immediately after application of sewage sludge followed by a rapid decrease. Taking into account the uncertainties related to the occurrence levels, and the rapid degradation in soil, VKM considers octylphenols, nonylphenols and LAS to be of low concern.

It is unlikely that antibacterial resistance may be promoted in the STP water, in the sludge or in the soil following application of sewage sludge as fertilizer. An exception may be a potential development of resistance to the fluoroquinolone ciprofloxacin in soil due to the persistence and limited mobility of these substances into the subsoil.

VKM was asked to assess the risk for seven inorganic compounds (cadmium, lead, mercury, nickel, zink, cobber and chromium), organic compounds (phthalates, octylphenols and octylphenol ethoxylates, nonylphenols and nonylphenol ethoxylates, linear alkylbenzenesulfonate, polychlorinated biphenyls (PCBs) and polycyclic aromatic hydrocarbons (PAHs)) in addition to pharmaceuticals.

For these contaminants VKM was specifically asked to evaluate the potential risk of dispersal of sewage sludge for soil living organisms, the aquatic environment, grazing animals, animals eating feed based on plants from sludge-treated soil, children eating soil, and humans consuming drinking water, crop plants and/or meat affected by the use of sludge as soil conditioner, in total a list of 12 defined exposure routes.

The VKM Scientific Panel on Contaminants has been responsible for this risk assessment.

The risk assessment was published 24.08.2009


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