Two recent scientific studies supported by PARC shed new light on how chemicals from our daily lives enter wastewater and what this means for environmental protection and public health. Using advanced high-resolution mass spectrometry and innovative data-analysis techniques, researchers mapped thousands of chemical signals in wastewater influent and effluents, uncovering clear patterns of discharge from households, rainfall events and outdoor runoff. Together, these findings offer a more accurate picture of how emerging contaminants move through urban water systems and how monitoring strategies can be improved. 

Daily rhythms hidden in wastewater 

In one study ↗, scientists collected hourly influent samples over three 24-hour periods from a medium-sized wastewater treatment plant. More than 72,000 chemical features were detected, including 402 identified compounds such as pharmaceuticals, personal care products, pesticides, and industrial chemicals.

By applying temporal clustering methods, researchers discovered five distinct daily patterns of chemical discharge: 

• Morning peak cluster – linked to human urine

Many pharmaceuticals and human metabolites peaked between 6:00 and 9:00, matching the well-known “first morning void”. The cluster included antidepressants, antipsychotics, antiepileptics and their metabolites, as well as compounds later confirmed through structure-elucidation (e.g., quinine and 3-hydroxyquinine). This pattern provides strong evidence that certain chemicals originate directly from internal human exposure.

• Daytime activities cluster – linked to household use

Compounds associated with cleaning agents, personal care products and common medications increased between 10:00 and 20:00, broadly reflecting showering, washing and general daily routines.

• Background clusters – influenced by rain and runoff

Three additional clusters had no clear daily cycle. During a documented rain event, chemicals linked to road runoff, including rubber additives and their degradation products, rose sharply, while other compounds were diluted. These findings demonstrate that high-resolution sampling can distinguish different chemical sources more accurately than traditional 24-hour composite samples, which sometimes miss peak concentrations by a factor of 10. 

Tracking contaminants in wastewater effluents 

A second study ↗ focused on wastewater treatment plant effluents and used a multichromatographic platform (LC, SFC and GC×GC) to detect more than 300 contaminants of emerging concern, including many highly polar or non-pharmaceutical substances often overlooked in routine monitoring. 

Key findings include:

• Rainfall significantly changes effluent composition, introducing clusters of contaminants from surface runoff and retention basin discharges.
• Persistent pollutants, such as PFAS, showed strong intragroup correlations, reflecting their shared sources and environmental resistance.
• Easily degradable compounds varied strongly during rain events, suggesting that removal efficiency fluctuates with changing flow conditions.

These results highlight the importance of analysing both dry- and wet-weather conditions to better understand pollutant pathways and optimise treatment strategies for each wastewater treatment plant.

Together, these studies demonstrate that wastewater carries a highly dynamic and complex mixture of chemicals; high-resolution sampling and clustering techniques can reveal clear behavioural, environmental and infrastructural patterns behind chemical emissions and that distinguishing chemicals linked to human excretion, household activities, industrial sources, or rainfall-driven runoff is essential for improving environmental monitoring and exposure assessment.