When discussing human impact on the environment, the focus is often on the global and national levels. But the impact can also be a major problem at the local level, resulting in poor environmental quality inside a few blocks of a city or a small stretch of river. Perhaps more than ever, man-made environmental problems can pose serious problems for potential homebuyers in various local markets.

Man-made environmental concerns can include poor air quality, a high number of environmental hazards, and, in the worst cases, high-concern superfunds. Superfund is a government environmental program established to identify hazardous waste sites for cleanup. Such issues were first brought to Americans’ attention in the late 1970s when environmental concerns surfaced in Love Canal, a community in upstate New York. Based on data from Homefacts, a U.S. housing market tracking company, these are the 10 housing markets with the worst man-made pollution.

Click here to see the most polluted housing markets in America

It can be extremely difficult to gauge the effects of man-made hazards. The ramifications of such hazards on both the environment and local economies may not be understood for many years if not decades. In addition, homebuyers do not necessarily take environmental hazards into account when selecting a home to purchase. Still, cleaner markets “that do not have high prevalence of these hazards tend to be just more stable real estate markets,” said Daren Blomquist, vice president of RealtyTrac, a housing data and analytics firm and the parent company of Homefacts.

Homefacts considered air quality, the presence of superfund sites, and the total number of environmental hazards per square mile in determining the markets with the worst man-made pollution.

Air quality was measured by the average percentage of days per year, since 2008, in which levels of carbon monoxide, ozone, nitrogen dioxide, particulate matter, and other toxic substances were above a certain threshold. While air quality across the country was considered poor only 5.4% of the time, five counties with the worst man-made pollution had poor air quality more often In Jackson County, Missouri, where air quality was among the worst of any county reviewed, the air quality was considered poor more than 12% of the time.

In addition to air quality, homebuyers may also care about the prevalence of environmental hazards in their cities. Six of the 10 housing markets with the most man-made pollution also had among the 10 highest concentrations of environmental hazards per square mile.

Some markets had especially high concentrations of particular hazards. For instance, St. Louis, Baltimore and Philadelphia County were all among the top five markets by brownfield sites per square mile. Brownfields are real estate properties for which redevelopment is hindered by the presence of hazardous waste. Another hazard is illegal drug labs. The environmental hazard score of Tulsa County, Oklahoma rose because of the relative presence of former drug labs, which pose serious environmental and safety concerns for nearby homeowners.

Since hazardous waste sites are so numerous and the danger levels are so varied, some superfund sites are placed on the national priorities list (NPL), which is designed to guide the Environmental Protection Agency’s (EPA) investigations and cleanup efforts. As Blomquist explained, if the superfund site has been identified, “it is more of a long-term problem … A lot of times the damage has already been done.”

Six of the markets with the worst man-made pollution had among the 10 most superfund sites on the national priority list, three of which were in New Jersey. Two of these New Jersey markets, Essex County and Hudson County, had the first- and second-highest concentrations of NPL superfunds in the nation, respectively.

Perhaps counterintuitively, markets with a higher prevalence of man-made hazards had stronger home price appreciation in recent years, according to RealtyTrac. Such markets may be more volatile also because of factors not related to pollution. These markets “have more people, so they’re more dynamic, [with higher] turnover in population and in buying and selling of homes,” Blomquist said. He added that over a longer period of time, home prices and appreciation rates were actually greater in markets with the lowest environmental concerns.

While factors other than environmental quality tend to play a much greater role in homebuyers’ decisions, Blomquist recommends homebuyers do the due diligence on the environmental quality of their area as well. “In that 1% of instances where there is that really serious [environmental] issue that affects you personally,” Blomquist said, such due diligence really matters.

In order to determine the 10 housing markets with the worst man-made pollution, 24/7 Wall St. reviewed data published by Homefacts, a RealtyTrac subsidiary. Only counties with a population of 100,000 or more were considered.

Homefacts collected data across three different broad metrics. Air quality accounted for 20% of a market’s score. Air quality scores are based on annual reporting, from 2008 onwards, on levels of airborne of carbon monoxide, fine particles and particulate matter, nitrogen dioxide, ozone, and sulfur dioxide. Superfunds that made the NPL accounted for 20% of a housing market’s score as well. Environmental hazards such as superfunds not on the NPL, as well as brownfields, former drug labs, and designated polluters accounted for 60% of each market’s total score. Homefacts used data from the EPA for most of these measures, with figures on drug labs coming from the Drug Enforcement Administration (DEA).

Median home prices are from RealtyTrac for July 2014. RealtyTrac also provided home price changes over one-, five-, and 10-year periods. Where available, home sales price data were utilized. For states that do not require disclosure sales information, or that had insufficient data, home list prices were used to calculate the median home prices. Annual median household incomes for 2014 are based on RealtyTrac’s extrapolation of U.S. Census Bureau data and represent an estimate. Unemployment data for June 2014 come from the Bureau of Labor Statistics.

These are the 10 most polluted housing markets

10. Tulsa County, Okla.
> Score: 17.7
> Pct. of days with bad air: 7.57% (131st highest)
> Hazards per sq. mile: 2.39 (6th highest)
> Median home price: $47,734 (219th lowest)

Tulsa County is one of the most environmentally hazardous housing markets in the nation, largely because of the prevalence of former illegal drug labs. In fact, no county with a population of 100,000 or more had a greater concentration of former drug labs than Tulsa County, with 1.7 labs per square mile. Such drug labs pose a major man-made environmental hazard, especially when methamphetamine is being produced. The Justice Department noted that a meth lab can produce between five to seven pounds of hazardous waste for every pound of methamphetamine it manufactures. According to the National Parks Service, “abandoned meth labs are basically time bombs, waiting for the single spark that can ignite the contents of the lab.” However, drug labs are not the only problem in Tulsa County, which also scores poorly for the number of brownfields and designated polluters per square mile.

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9. Jackson County, Mo.
> Score: 18.6
> Pct. of days with bad air: 12.37% (15th highest)
> Hazards per sq. mile: 1.12 (23rd highest)
> Median home price: $44,493 (138th lowest)

Jackson County is one of several urban areas in Missouri with unhealthy levels of man-made environmental damage. The level of air pollution in Jackson County was determined to be harmful during more than 12% of the time, more than in all but a handful of counties reviewed. Although it’s not clear how environmental factors affect local economic growth, the prevalence of hazardous materials does have an negative effect on communities over time. Like many polluted areas, the Jackson housing market is characterized by high unemployment and low incomes. Roughly 7.5% of the county’s workforce was unemployed last year, and a typical household makes an estimated $44,500 annually.

8. Middlesex County, N.J.
> Score: 19.6
> Pct. of days with bad air: 1.65% (182nd lowest)
> Hazards per sq. mile: 1.28 (18th highest)
> Median home price: $78,427 (41st highest)

Middlesex is one of three New Jersey counties among the 10 worst markets for man-made pollution. All three counties are located in the New York City metro area. One major factor is the concentration of superfund sites named to the EPA’s National Priorities List. These include the Middlesex Sampling Plant, where nuclear tests were conducted, as well as numerous landfills and chemicals plants. Most of the area’s environmental hazards, outside of superfunds, consist of designated polluters. Middlesex County had 0.5 designated polluters — facilities included in the EPA’s Toxic Release Inventory program — per square mile, more than in most of the markets reviewed.

7. Salt Lake County, Utah
> Score: 22.8
> Pct. of days with bad air: 11.87% (21st highest)
> Hazards per sq. mile: 0.53 (54th highest)
> Median home price: $59,329 (160th highest)

The air quality in Salt Lake County is considered hazardous during nearly 12% of the year, one of the worst ratings nationwide. The region’s air pollution problem is recognized by the county’s health department, and local officials have identified motor vehicles — responsible for roughly half of the particulate pollution — as a major culprit. As a result, the registration of vehicles less than six-years old in the Salt Lake Valley includes an annual emissions test. Salt Lake County residents are relatively well-off. Less than 4% of the area’s workforce was unemployed as of June, and a typical household earns an estimated $59,329 annually. Both figures were exceptionally good compared to other markets reviewed.

6. Philadelphia County, Pa.
> Score: 24.0
> Pct. of days with bad air: 1.39% (148th lowest)
> Hazards per sq. mile: 3.95 (2nd highest)
> Median home price: $35,593 (14th lowest)

While Philadelphia County has some of the worst levels of man-made pollution among all markets reviewed, the area has made considerable progress. For example, Metal Bank, a superfund site located on the Delaware river, was completely cleaned up in 2010. And the percentage of bad air days was far lower than the national average, at just 1.4% since 2008. However, local officials may still have their work cut out for them. Brownfield sites — sites that contain contaminants which potentially hinder their redevelopment — were more prevalent in Philadelphia than in all but one other county reviewed by RealtyTrac.

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5. Denver County, Colo.
> Score: 27.4
> Pct. of days with bad air: 10.58% (35th highest)
> Hazards per sq. mile: 1.58 (12th highest)
> Median home price: $50,900 (283rd lowest)

Denver County ranked high across most measures considered by Homefacts. More than 10.5% of days in the area were counted as bad air quality days, higher than in most counties. Both brownfields and designated polluters were also quite high per square mile. Denver County also had 0.22 former illegal drug labs per square mile, higher than in most counties. Illegal drug labs pose a serious environmental risk to nearby residents because they create hazardous waste and can result in explosions. However, homebuyers may not be that concerned with environmental issues. The median home price in Denver County was $295,000 in July, higher than in most large counties, and up a fairly healthy 6.1% from the year before.

4. Essex County, N.J.
> Score: 28.4
> Pct. of days with bad air: 1.52% (170th lowest)
> Hazards per sq. mile: 2.38 (7th highest)
> Median home price: $51,431 (285th highest)

Superfund sites are a major environmental problem in Essex County. The county had more superfund sites per square mile on the national priorities list than any other large housing market. One well-known problem site in the county is the Passaic River, which also serves as a border for Essex County. According to the EPA, “The sediments of the lower Passaic River…are contaminated with a variety of hazardous substances, including dioxin, PCBs, mercury, DDT, pesticides and heavy metals.” Plans to clean the Passaic River via dredging — removing sediment from the bottom of the river — carry a massive tab estimated at $1.7 billion. Essex County is part of the New York City metro area, which has numerous waterways that are categorized as superfund sites.

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3. Hudson County, N.J.
> Score: 30.3
> Pct. of days with bad air: 1.23% (127th lowest)
> Hazards per sq. mile: 3.15 (4th highest)
> Median home price: $58,599 (167th highest)

Hudson County lies across the Hudson River from New York City. It has among the most brownfields, at 0.43 per square mile. According to the EPA, using such sites for purposes such as building new residences “may be complicated by the presence or potential presence of a hazardous substance, pollutant, or contaminant.” In addition to the concerns residents face from brownfields, Hudson County also has one of the nation’s highest concentrations of superfunds in the U.S. However, this has not served as much of a deterrent to homebuyers, who are willing to pay quite a bit to live in the county. The median price of a home in Hudson County was $358,000 in July, higher than in most markets in America.

2. Baltimore City, Md.
> Score: 31.0
> Pct. of days with bad air: 1.13% (114th lowest)
> Hazards per sq. mile: 3.82 (3rd highest)
> Median home price: $38,947 (35th lowest)

The city of Baltimore is the second worst housing market for man-made pollution. According to clean water advocacy group Blue Water Baltimore, “As an industrial port, Baltimore is plagued with a history of toxic pollution.” Baltimore has nearly 1.5 designated polluters per square mile. The city trails just one other housing market, St. Louis for the number of polluters per square mile, identified through the EPA’s Toxic Release Inventory program. Baltimore was also among the worst markets for brownfields, with 0.74 per square mile. In all, the city ranked third-worst for the number of environmental hazards per square mile — which accounts for 60% of a market’s man-made pollution score — behind only Philadelphia County and St. Louis.

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1. St. Louis City, Mo.
> Score: 77.8
> Pct. of days with bad air: 7.89% (117th highest)
> Hazards per sq. mile: 13.30 (the highest)
> Median home price: $31,534 (3rd lowest)

The city of St. Louis is the nation’s worst housing market for man-made pollution. The city has 13.3 environmental hazards per square mile, according to Homefacts, by far the most of any housing market in the U.S. The fact that St. Louis led all large housing markets in both the number of brownfields and the number of designated polluters per square mile was a major contributing factor. Urban decay, deindustrialization, and population have long been problems in the city. As of June, 9.6% of the city’s workforce was unemployed, higher than in most markets. The city’s 2014 estimated median household income was just over $31,500, making St. Louis one of the poorest large markets.

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