ENSC 201 – Lecture 10: Drinking Water and Environmental Toxicology

How has human use of freshwater changed over the last 100 years?

Human use of freshwater has increased sixfold, leading to stress points and a feedback loop that accelerates water quality loss.

What does "potable" mean in terms of drinking water?

it means the water is free of toxicants and biological contaminants, making it safe for human consumption.

How does groundwater become naturally filtered?

It passes from the surface through layers of soil and rock, undergoing filtration and bacterial action that remove contaminants.

Why is surface water never considered safe for drinking without treatment?

It can contain biological and chemical contaminants and does not meet WHO guidelines unless treated.

Name five common waterborne bacterial pathogens

• Escherichia coli (STECs, including E. coli 0157:H7)

• Campylobacter jejuni

• Vibrio cholerae

• Salmonella typhi

• Legionella pneumophila

What are the primary sources of pathogens in drinking water?

• Agricultural runoff

• Manure/natural fertilizers

• Community sewage systems

• Septic systems and latrines

• Wildlife

What is the purpose of testing for E. coli in drinking water?

E. coli is used as a fecal indicator because its presence correlates with other fecal-source pathogens.

What is the global impact of unsafe drinking water?

• 800 million people lack access to potable water.

• 2.1 billion people are highly vulnerable to waterborne diseases.

• 34,000 deaths daily from water-related diseases.

Why is biological contamination a major concern in low-income countries?

80% of diseases in these regions are water-related and preventable, including diarrhea (2.2 million deaths annually).

What are common failures of drinking water treatment in high-income countries?

• Poor maintenance (e.g., Walkerton, Ontario, 2000).

• Testing delays (results take 1–3 days).

• Lack of proper chlorination.

What was the cause of the Walkerton, Ontario water crisis in 2000?

• Agricultural runoff contaminated a faulty well.

• The chlorinator was broken.

• Test results were delayed and ignored.

What technological improvements were made in response to water safety failures?

• On-site water testing developed by Queen’s University (TECTA-PDS).

• Automated systems provide results in 2–18 hours, eliminating long lab delays.

Where is IDEXX TECTA headquartered, and what is its purpose?

It is headquartered in downtown Kingston and focuses on water testing technology to minimize costs, taxes, and infrastructure deficits.

What was the key issue in the Flint, Michigan water crisis (2015)?

• The city changed its water source to save money.

• Differences in water chemistry were not considered.

• Lead levels reached 2,000–13,000 ppb (above 5,000 ppb is hazardous waste).

• Failures in monitoring and distribution systems worsened the crisis.

What are disinfection byproducts (DBPs) in drinking water?

Chemical compounds formed when disinfectants like chlorine react with organic matter, e.g., trihalomethanes (THMs).

Why is chlorine added to drinking water, and what are the risks?

• Kills biological contaminants.

• Can allow pathogens through if source water quality is poor.

• Creates trihalomethanes (THMs), which are possible carcinogens.

What factors increase THM formation in drinking water?

• High levels of dissolved organic carbon (DOC), such as from algae.

• Chlorination processes.

• Poor source water quality.

What are the potential health effects of THMs?

• Possible carcinogenic effects (classified by IARC).

• Can cause DNA methylation, leading to uncontrolled cell growth and loss of DNA repair mechanisms.

What are some water treatment concerns in high-income vs. low-income communities?

• Low-income communities: Need access to safe water due to lack of treatment infrastructure.

• High-income communities: Generally have safe water but face secondary issues like DBPs.

What are some modern water treatment solutions?

• Local treatment (point-of-use systems like filters, UV, and reverse osmosis).

• Bottled water, though it has higher environmental impacts.

Why do experts recommend tap water over bottled water?

• Bottled water has a larger environmental impact (waste, energy use).

• Tap water in Canada generally meets safety standards.

• Better governance and accessibility of water resources.

What enables wastewater (WW) to be treated and reused?

Reverse osmosis (RO) and other advanced treatment technologies.

What is the purpose of water reuse in water-stressed areas?

• omplements desalination efforts.

• Returns treated sewage/WW to reservoirs for drinking water.

• Creates a closed-loop water recycling system.

What is the main challenge in wastewater reuse for drinking water?

• Public perception, known as the "toilet-to-tap" stigma.

• Many reuse projects initially supply agriculture and industry.

• Increasingly, jurisdictions are adding treated reuse water back into drinking supplies.

What is Wastewater Surveillance for Reuse?

• A public health strategy that monitors pathogens and contaminants in wastewater.

• Supports wastewater-based epidemiology (WBE).

How has wastewater surveillance contributed to public health in Ontario?

• Used as a primary tool for tracking SARS-CoV-2 (COVID-19) trends from Jan 2022 - Jul 2024.

• KFL&A Public Health dashboard posts wastewater case estimates.

• Expanded in 2023-24 to track Flu and RSV

What are the challenges with conventional wastewater pathogen detection?

• Takes 4-5 days and requires high labor costs.

• Newer molecular methods (PCR, sequencing) take 1-2 days but remain expensive.

What is the connection between wastewater and antimicrobial resistance (AMR)?

• Wastewater can contain resistant microbes and genes (KPC, NDM, OXA-48, VIM).

• Monitoring is critical for One Health approaches.

What is the One Health approach in water management?

• Connects human health, agriculture, and ecosystems.

• Focuses on the multidirectional flow of resistant microbes and genes.

What are the key takeaways from wastewater treatment research?

• Water resources are under stress, impacting health.

• Source water protection is critical.

• Aging infrastructure and cost constraints create risks.

• Drinking water may have unknown health impacts, requiring continued research and surveillance.