Synthetic chemicals with an extremely stable carbon-fluorine bond — one of the strongest in chemistry. Developed in the 1940s for use in firefighting foam, non-stick coatings, food packaging, and stain-resistant textiles. They do not break down in the environment or the human body.

Two of the most studied — PFOA and PFOS — have been phased out but persist widely. Over 12,000 PFAS compounds exist; most have little toxicological data.

Thyroid disruption, immune suppression (reduced vaccine response in children), increased cholesterol, kidney and testicular cancer (PFOA/PFOS), and developmental harm during pregnancy. Effects occur at very low concentrations — EPA's 2024 MCL for PFOA and PFOS is 4 parts per trillion.

New Jersey (highest PFAS burden in North America — Dupont/Chemours legacy, dense industrial sites, concentrated monitoring). Michigan (PFAS plumes from military bases — Camp Grayling, Selfridge ANGB). North Carolina (Chemours Fayetteville Works — GenX contamination of Cape Fear River). Minnesota (3M manufacturing legacy in Twin Cities metro).

Canada: British Columbia (firefighting foam use at airports — Vancouver International, CFB Comox). Ontario (industrial corridors). Quebec (Montreal metro area, industrial legacy).

Nitrogen compounds that enter groundwater primarily from synthetic fertilisers, animal manure, and septic systems. In agricultural regions, seasonal application cycles mean nitrate levels spike in spring and early summer.

Methemoglobinemia ("blue baby syndrome") in infants under 6 months — nitrates interfere with blood oxygen transport. Emerging evidence links long-term adult exposure to colorectal cancer, thyroid disruption, and adverse birth outcomes at levels below the current 10 mg/L standard.

Iowa, Illinois, Indiana, Nebraska (Corn Belt — highest nitrate loading nationally; Des Moines Water Works operates the largest nitrate removal system in the world). Kansas and South Dakota (High Plains Aquifer contamination). Central Valley California (intensive vegetable and dairy agriculture — some of the highest nitrate concentrations in North America).

Canada: Manitoba and Saskatchewan (grain and livestock belt — nitrate loading from both fertiliser and livestock). Southern Ontario (intensive agriculture — some areas exceed Health Canada guideline of 10 mg/L).

Naturally occurring elements that concentrate to harmful levels through geological processes, mining, smelting, coal combustion, and agricultural inputs. Arsenic leaches from rock into groundwater. Mercury cycles through coal combustion and bioaccumulates in fish tissue. Cadmium enters soil via phosphate fertilisers and atmospheric deposition.

Arsenic: skin lesions, bladder and lung cancer, cardiovascular disease, developmental harm — classified Group 1 carcinogen (IARC). Mercury: neurological damage, particularly during fetal development and early childhood. Cadmium: kidney damage, bone loss, lung cancer with long-term inhalation.

Arsenic: New England (granite bedrock — Maine, New Hampshire, Vermont have highest private well arsenic nationally); Nevada, Arizona (desert geologic sources); Mountain West states (mining legacy). Mercury: Great Lakes states (atmospheric deposition + legacy industrial); Gulf Coast states (fish advisories). Cadmium: Zinc Belt (Missouri, Kansas, Oklahoma — smelting legacy).

Annual average fine particulate matter (PM2.5 — particles smaller than 2.5 microns) and ground-level ozone burden, drawn from EPA AQS monitoring networks and American Lung Association State of the Air data. PM2.5 penetrates deep into lung tissue and enters the bloodstream. Ozone forms when vehicle and industrial emissions react with sunlight.

PM2.5: cardiovascular disease, stroke, lung cancer, premature death — no safe exposure level identified by WHO. Ozone: asthma attacks, reduced lung function, aggravated respiratory conditions. Children, elderly, and people with existing conditions face disproportionate risk.

California (Central Valley — Bakersfield, Fresno, consistently among worst PM2.5 nationally; Los Angeles basin for ozone). Industrial Midwest: Ohio, Indiana, Illinois, Michigan (steel, auto, coal). Pennsylvania (Pittsburgh metro — Allegheny County regularly fails both PM2.5 and ozone standards).

Canada: Lower Fraser Valley BC (trapped by mountains — Metro Vancouver airshed). Southern Ontario (Toronto-Hamilton corridor — industrial and traffic emissions). Fort McMurray AB (oil sands operations).

Composite burden of agricultural pesticide application intensity (USGS NAWQA, USDA NASS) and groundwater pesticide detections. Atrazine (corn herbicide) is the most common groundwater contaminant in the US. Chlorpyrifos and organophosphate insecticides are the highest neurological-risk compounds in this layer.

Atrazine: endocrine disruption, possible carcinogen. Chlorpyrifos: developmental neurotoxicity in children — reduced IQ, ADHD — EPA revoked all food tolerances in 2021. Glyphosate: IARC Group 2A probable carcinogen, though regulatory assessments remain contested. Cumulative low-dose exposures are poorly characterised.

Iowa, Illinois, Nebraska, Indiana, Ohio (Corn Belt — atrazine, acetochlor, metolachlor; among the highest application rates in the world). California (Central Valley — most diverse pesticide use nationally; almonds, grapes, strawberries, tomatoes). Louisiana (sugarcane and rice — high fungicide and herbicide load).

Canada: Saskatchewan and Manitoba (canola, wheat — glyphosate dominant). Ontario (corn and soybean belt — atrazine detections in groundwater).

Plastic particles under 5mm — including nanoplastics under 1 micron — from fragmentation of larger plastics, synthetic textile washing (microfibers), tire wear, and industrial processes. Found in tap water, bottled water, food, air, and human blood, lung tissue, and placentas.

Toxicological understanding is rapidly developing. Physical particles cause inflammation; chemical additives (plasticisers, flame retardants, stabilisers) are endocrine disruptors. A 2024 NEJM study found microplastics in carotid artery plaques associated with increased cardiovascular events. WHO (2022): insufficient data to establish a health-based guideline value, but monitoring urgently recommended.

Great Lakes region: Lake Erie has the highest measured microplastic concentration of any freshwater body globally. Chicago and Detroit metro areas show highest tap water concentrations in USGS monitoring. Pacific Coast: atmospheric deposition from ocean gyres measurable in remote areas of Oregon and Washington.

Canada: Great Lakes Ontario and Quebec shorelines. BC coast (North Pacific Gyre proximity). Arctic: atmospheric transport means remote communities show detectable levels — Health Canada monitoring ongoing.

Organic compounds resistant to environmental degradation — they persist in soil, water, and living tissue for decades. The "dirty dozen" (Stockholm Convention) includes PCBs (electrical transformers), dioxins (industrial combustion byproducts), DDT, and chlordane. Most are banned but remain widespread due to environmental persistence and bioaccumulation through food chains.

Carcinogenicity, endocrine disruption, immune suppression, reproductive harm, developmental neurotoxicity. Dioxins are among the most toxic substances known — measured in picograms. POPs concentrate in fatty tissue and magnify at each food chain level — top predators (large fish, marine mammals, humans who eat them) reach the highest exposures.

Great Lakes states: PCB contamination from industrial manufacturing (GE Hudson River, Fox River Wisconsin). Gulf Coast: legacy pesticide contamination from agriculture. Arctic regions: atmospheric and oceanic transport means Arctic Indigenous communities have some of the highest body burdens globally — traditional diets of marine mammals concentrate POPs at the top of long food chains.

Composite of lead service line density (NRDC 2024 national estimate), pre-1940 housing stock (highest lead paint risk), and blood lead surveillance data (CDC NHANES, NIOSH ABLES). Lead enters drinking water through corrosion of service lines and interior plumbing, and children ingest it through paint dust and chips in older housing.

No safe level of lead exposure for children — CDC reference value is 3.5 µg/dL blood lead. Effects: permanent IQ reduction, ADHD, behavioural problems, hearing loss. Adults: cardiovascular disease, hypertension, kidney damage. EPA's Lead and Copper Rule Improvements (2024) require utilities to replace all lead service lines within 10 years.

Illinois (Chicago required lead service pipes until 1986 — highest density nationally). Michigan (Flint crisis context; Detroit still replacing lines). Ohio and Pennsylvania (industrial cities — Cleveland, Pittsburgh, Erie have high LSL density and old housing stock). New Jersey (high LSL density, dense pre-1950 housing).

Canada: Quebec (Montreal — lead service lines in older neighbourhoods; Quebec allowed lead pipes until 1970). Ontario (pre-1955 housing, particularly Hamilton, Windsor).

Rate and severity of Safe Drinking Water Act health-based violations per utility, aggregated to state level, weighted by population served. Includes maximum contaminant level (MCL) violations, treatment technique violations, and significant monitoring/reporting failures. Disinfection byproducts (trihalomethanes, haloacetic acids) — formed when chlorine reacts with organic matter — are a major contributor to violations in surface water systems.

Depends on violation type. MCL violations indicate regulated contaminants above legal limits. DBPs are associated with bladder cancer and adverse pregnancy outcomes with long-term exposure. Total coliform violations signal potential pathogen contamination. Note: violation rates reflect regulatory compliance, not necessarily the full picture of chemical exposures not yet regulated.

Texas (largest number of violations by volume — many small systems serving rural communities lack resources for compliance). Pennsylvania (significant DBP violations in older surface water systems). West Virginia (industrial contamination history — 2014 Elk River chemical spill). Rural states generally: small systems serving fewer than 500 people account for the majority of US violations, disproportionately affecting rural and low-income communities.

A naturally occurring radioactive gas produced by uranium decay in soil and rock. It seeps into buildings through foundation cracks, sump pits, and gaps around pipes. It's colourless, odourless, and undetectable without a test. Radon decays into radioactive particles that lodge in lung tissue when inhaled.

Second-leading cause of lung cancer after smoking — responsible for approximately 21,000 US deaths and 3,300 Canadian deaths annually. Risk is significantly elevated in smokers exposed to radon. EPA action level: 4 pCi/L. Health Canada guideline: 200 Bq/m³ (approximately 5.4 pCi/L). WHO recommends action above 100 Bq/m³ where feasible.

Alaska (10.7 pCi/L average); South Dakota (9.6); Pennsylvania (8.6 — nearly all counties Zone 1); Ohio (7.8 — Ohio Shale geology); Washington (7.5 — glacial uranium-bearing deposits); Kentucky and Montana (7.4 each); Iowa (entirely Zone 1 — 70%+ of homes above EPA action level, glacial radium deposits).

Canada: Manitoba (168 Bq/m³ average, 1 in 3 homes above guideline); Saskatchewan (140 Bq/m³); Yukon and Atlantic Canada (1 in 3 homes above guideline — granitic bedrock). BC coastal zone: 1 in 75 homes — among the lowest in North America.

The unweighted arithmetic mean of all ten individual layer scores. It answers: which regions face elevated contamination across the broadest range of categories simultaneously? A region scoring moderate on seven layers carries a different real-world risk profile than one with a single extreme value — cumulative exposure to multiple contaminants produces effects not predicted by assessing each chemical alone.

No weighting is applied — there is no scientifically defensible basis to declare one contaminant universally more important than another without making value judgements this index declines to make.

Illinois (70) — highest nationally. Lead service line density (Chicago required lead pipes until 1986), corn belt nitrates and pesticides, Great Lakes microplastics and POPs, PFAS contamination. Compound burden across almost every category.

Ohio and Pennsylvania (69) — industrial corridor air quality, coal legacy heavy metals, Great Lakes contamination, significant radon, lead infrastructure burden.

New Jersey (66) — highest PFAS burden nationally, significant lead and POPs legacy, elevated microplastics in a dense small-area population.

EPA's Framework for Cumulative Risk Assessment (2003) established that co-exposures to multiple chemicals can produce additive or synergistic health effects beyond what individual assessments predict. Research consistently finds that low-income communities and communities of colour bear disproportionate cumulative burdens — more likely to live near multiple pollution sources simultaneously.

Hawaii (32) — near-zero radon, no industrial corridor, limited agricultural chemical loading, modern infrastructure.

Vermont (38) — protected watersheds, low industrial pressure, strong regulation, genuine low burden across most categories.

Nunavut (36) — minimal local sources, but atmospheric deposition and bioaccumulation mean Indigenous community exposure is substantially higher than the population-wide average.

Computed directly from the ten individual layer values. The Water Quality layer (inverted in display) is included in its raw form — high value = greater burden — so poor tap water compliance correctly adds to cumulative score.