On the disposal of sewage sludge with radioactive contamination

There is no radiobiological hazard of concern in the spreading of sewage sludges with radioactivities such as encountered in Northwest Germany since May 1986 onto the arable land. As a rule of thumb the spreading per m2 will aproximately duplicate the radioactivity originally deposited by direct fallout. The plowing and/or tilling of the soil dilutes the radioactivity appreciably, and only a small fraction of the resulting modest soil radioactivity is transfered to plant biomass via the roots. The distribution of a sludge radioactivity of 30,000 Bq/kg TS in the 20 cm top layer of the ground is expected to lead to an effective additional radiation exposure of about 18 mrem per capita over the next 50 years. This is an entirely negligible amount. When sewage sludges are presently spread onto meadows, a higher amount of sludge radioactivity is transferred to plant biomass and from there to milk and meat. Because of a lack of experimental data this transfer is more difficult to estimate. As judging from the available data, the effective additional radiation exposure resulting from the spreading of 0.5 kg (TS)/m2 of sewage sludge (30,000 Bq/kg TS) onto meadows will probably be in the order of 1-10 mrem per capita and year. (orig.)