This document discusses contaminants of emerging concern and the challenges they pose. There are over 100,000 chemicals in commerce that can each form over 10 transformation products, totaling over 20 million possible chemical structures in the environment. Given the vast number of potential chemical exposures and combinations, fully assessing risks is extremely difficult. While treatment plant upgrades have reduced acute ecological impacts of effluents, chronic low-level exposures from chemical mixtures are harder to evaluate. Improving chemical detection methods and toxicity data is crucial for better risk assessments. Unknown chemical structures and interactions remain a challenge, requiring simplified assessment approaches. Open data sharing and adaptive management can help address unknown risks.

1. Contaminants of Emerging Concern
Known knowns
Known unknowns
Unknown unknowns
Thomas Backhaus
University of Gothenburg
thomas.backhaus@gu.se

2.  100 000 chemicals in commerce,
10 transformation products from each
 20 million species
 22 000 billion exposure scenarios,
without considering
– different concentrations,
– simultaneous occurrence of chemicals,
– any type of ecological interactions
Scope of the issue

4. Speed of regulatory risk assessments…
 42 new chemicals
discovered per hour
 100 000 chemicals used in
commerce
 Each chemical is
transformed in dozens of
degradation products
 22 000 billion exposure
scenarios
G. M. Gray & J.T. Cohen (2012): Rethink chemical risk assessments, Nature

5.  Compliance Review of 1814 REACH dossiers for high-
production volume chemicals by the German Institute for
Risk Evaluation / Environmental Protection Agency
(BfR/UBA)
 Number of fully REACH-compliant datasets: 1
 42% are „complex“, i.e. an assessment was not possible
 58% showed definite deficiencies
Quality of risk assessments…

6. 7
Successful STP-Upgrade in Switzerland

7. 8
STP-Upgrade at Herisau (Switzerland)
2014
2016
DownstreamUpstream

8. STP-Upgrade shows that effluents do not
cause ecological impacts any more
 Non-upgraded STPs:
clear differences
up/downstream
 Upgraded STP:
up/downstream
communities are
identical-
Effluent from the
upgraded STP does not
cause ecological impacts

9. Chemical/analytical power is crucial
Moschet et al. (2014). How a complete pesticide screening changes the assessment of surface water quality. Environmental
science & technology, 48(10), 5423-5432.

10. Insufficient chemical/analytical power
Gustavsson, et al. (2017) Pesticide mixtures in the Swedish streams: Environmental risks, contributions of individual
compounds and consequences of single-substance oriented risk mitigation, Science of the Total Environment. 973–983.

11. Transformation does not always imply
detoxification
Oxidation of Ethinylestradiol
Transformation product has a higher estrogenicity than the parent compound
Cwiertny, et al. (2014) ‘Environmental designer drugs: When transformation may not eliminate risk’, Environmental
Science and Technology, 48(20), pp. 11737–11745.

12. Known knowns
 CEC are ubiquitous
 Infinite number of possible chemical structures
 Occur as complex chemical mixtures
 From point-sources causing acute effects to a
blanket of exposure with chronic, subtle effects
 Analytical power and biological testing methods
define final risk estimates
 Removal rate is a limited indicator for risk mitigation

13. Known unknowns
 Chemical structures
 Toxicology and ecotoxicology
 Use & emission pathways
 Exposure
 Risk

14. Conclusions – known unknowns
 Simplifications needed
• (eco)TTC
• QSAR/read-across
• Groupwise assessment
• Lead compounds
 Publically available data repositories
 Data quality
 Holistic approaches
 Better harmonization
 Water systems “binning”

15. Unknown unknowns

16. How to act on Unknown Unknowns
 Chemicovigilance, incidence reporting, postmarket
monitoring
 Adaptive management
 Publically available quality-assured data
 Science communication
 Toxicant-free environment vs. non-toxic environment
 Cost-benefit assessments

17. Contaminants of Emerging Concern
–
From Point Source Priority Pollutants
to
Life, the Universe and Everything Else
Thomas Backhaus
University of Gothenburg
thomas.backhaus@gu.se
@ThoBaSwe