A preliminary study on the ecotoxic potency of wastewater treatment plant sludge combining passive sampling and bioassays

Heidi Ahkola, Petra Lindholm-Lehto, Noora Perkola, Pia Välitalo, Päivi Meriläinen, Kimmo Mäenpää, Julio Alberto Alegre Stelzer, Ilse Heiskanen, Johanna Järvistö, Jari Nuutinen, Matti T. Leppänen

Research output: Contribution to journalArticleScientificpeer-review


Sewage sludge is an inevitable byproduct produced in wastewater treatment. Reusing nutrient-rich sludge will diminish the amount of waste ending in soil dumping areas and will promote circular economy. However, during sewage treatment process, several potentially harmful organic chemicals are retained in sludge, but proving the safety of processed sludge will promote its more extensive use in agriculture and landscaping.

Environmental risk assessment of sludge requires new methods of characterizing its suitability for various circular economy applications. Bioavailable and bioaccessible fractions are key variables indicating leaching, transport, and bioaccumulation capacity. Also, sludge treatments have a significant effect on chemical status and resulting environmental risks. In this study, the concentrations of polyaromatic hydrocarbons (PAHs), triclosan (TCS), triclocarban (TCC), methyl triclosan (mTCS), and selected active pharmaceutical ingredients (APIs) were determined in different sludge treatments and fractions. Passive samplers were used to characterize the bioavailable and bioaccessible fractions, and the sampler extracts along the sludge and filtrate samples were utilized in the bioassays.

The TCS and PAH concentrations did not decrease as the sludge was digested, but the contents diminished after composting. Also, mTCS concentration decreased after composting. The API concentrations were lower in digested sludge than in secondary sludge.

Digested sludge was toxic for Aliivibrio fischeri, but after composting, toxicity was not observed. However, for Daphnia magna, passive sampler extracts of all sludge treatments were either acutely (immobility) or chronically (reproduction) toxic. Secondary and digested sludge sampler extracts were cytotoxic, and secondary sludge extract was also genotoxic. The measured chemical concentration levels did not explain the toxicity of the samples based on the reported toxicity thresholds.

Bioassays and sampler extracts detecting bioavailable and bioaccessible contaminants in sludge are complementing tools for chemical analyses. Harmonization of these methods will help establish scientifically sound regulative thresholds for the use of sludge in circular economy applications.
Original languageEnglish
Article number143700
Number of pages14
JournalScience of the Total Environment
Early online date23 Nov 2020
Publication statusE-pub ahead of print - 23 Nov 2020
MoE publication typeA1 Journal article-refereed


  • passive sampling
  • bioaccessibility
  • bioavailability
  • sewage sludge
  • toxicity
  • digestion
  • composting
  • risk assessment
  • PAHs
  • APIs

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