other wastes including other individuals' urine as they travel to a municipal wastewater treatment plant. The wastewater is sampled at the plant's inlet, prior to treatment. This is typically done with autosampler devices that collect 24-hour flow or temporally composite samples. These samples contain biomarkers from all the people contributing to a catchment. Collected samples are sent to a laboratory, where analytical chemistry techniques (such as liquid chromatography-mass spectrometry) are used to quantify compounds of interest. These results can be expressed in per capita loads based on the volume of wastewater. Per capita daily consumption of a chemical of interest (e.g. a drug) is determined as where R is the concentration of a residue in a wastewater sample, F is the volume of wastewater that the sample represents, C is a correction factor which reflects the average mass and molar excretion fraction of a parent drug or a metabolite, and P is the number of people in a wastewater catchment. Variations or modifications may be made to C to account for other factors such as the degradation of a chemical during its transport in the sewer system. Applications Commonly detected chemicals include, but are not limited to the following; Cocaine Amphetamine Methamphetamine Methylone Ecstasy Heroin Alcohol Nicotine Caffeine Ketamine Opioids Antidepressants Antipsychotics Antimicrobials Antihistamines Aritificial sweeteners Temporal comparisons By analyzing samples taken across different time points, day-to-day or longer term trends can be assessed. This approach has illustrated trends such as increased consumption of alcohol and recreational drugs on weekends compared to weekdays. A temporal wastewater-based epidemiology study in Washington measured wastewater samples in Washington before, during and after cannabis legalisation. By comparing cannabis consumption in wastewater with sales of cannabis through legal outlets, the study showed that the opening of legal outlets led to a decrease in the market share of the illegal market. Spatial comparisons Differences in chemical consumption amongst different locations can be established when comparable methods are used to analyse wastewater samples from different locations. The European Monitoring Centre for Drugs and Drug Addiction conducts regular multi-city tests in Europe to estimate the consumption of illegal drugs. Data from these monitoring efforts are used alongside more traditional monitoring methods to understand geographical changes in drug consumption trends. Microbial surveillance Virus surveillance Sewage can also be tested for signatures of viruses excreted via feces, such as the enteroviruses poliovirus, aichivirus and coronavirus. Systematic wastewater surveillance programs for