5. Conclusion
By increasing the nitrogen supply, sewage sludge may have
indirect effects on plant growth. Any bioaccumulated TM would be
diluted in the presence of greater biomass tissue, at which point no
adverse effects would occur. In this study, SS application increased
the nutrient and TM amounts in the soils which were less
susceptible to leaching toward deeper soil layers. However, a
distinction should be made between the sludge rates with respect
to nutrient availability in order to avoid excessive application of
sludge. Since the differences between the 30S and 60S treatments
were not significant, the lower rate should be sufficient to fertilize
young larch. Though this study establishes the benefits of
municipal SS and demonstrates that the risks involved are
minimal, further studies are needed to determine long-term TM
behavior in the soil–plant continuum, with emphasis on assessing
the potential transfer into groundwater and from there into the
food chain.