Every day, in cities across the country, businesses open up, close down, or move to new locations. And every day, in those very same cities, people move in and people move out. A once-industrial neighborhood is reinvented as a trendy hot spot populated by new restaurants and young professionals in search of loft apartments; a formerly low-income neighborhood of modest bungalows is gradually taken over by gentrifying upper-income young families.

In the book Sites Unseen: Uncovering Hidden Hazards in American Cities, sociologists Scott Frickel and James R Elliott confront an often-overlooked environmental consequence of these changes: buried underneath America’s cities are hundreds of millions of pounds of hazardous waste, deposited there by businesses of all sizes. As Frickel and Elliott write, the federal government now estimates that almost 800m pounds of hazardous waste is released each year. (This figure excludes waste from metal mining.)

Some of these businesses are big factories located in well-known industrial areas and, as such, attract attention from activists, neighbors and government regulators. Others, however, are small businesses – modest enough that their activities may have gone unnoticed by both neighbors and regulators. Businesses such as these may have only been in operation for a few years before they closed down.

To identify these sites, Frickel and Elliott used historic state directories of manufacturers to construct a historically hidden industrial database for four river port cities: New Orleans, Philadelphia, Portland and Minneapolis. They then examine what the interaction of three distinct processes – industrial churning (the movement and flow of businesses around a city), residential churning (the movement of people around a city) and risk containment (regulatory policies that prioritize only visible hazardous sites for clean up) – means for the distribution of potential environment hazards in urban landscapes.

Frickel and Elliott sat down with Pacific Standard to answer questions about their book, the shortcomings of existing data sources on environmental hazards, and the implications of their research for city dwellers.

The United States does collect some data about hazardous sites – for example, the Environmental Protection Agency’s Toxics Release Inventory (TRI) data set, which you discuss in the book. What are the shortcomings of our existing data sources with respect to identifying all potentially hazardous sites in cities?

SF: Those databases have some very well-known and well-understood limitations. They didn’t start collecting this data until the mid-1980s, so everything that came before that ... simply didn’t make it into the database. These databases also put pretty strict parameters around what kinds of industrial sites or manufacturing processes they’re interested in. And there are both scientific and political reasons for those parameters. For example, with the TRI data, manufacturers that release less than a certain amount of pollution annually are exempted from reporting those releases, and that also holds true for manufacturing facilities that employ a relatively small number of people.

JE: All this reporting is also voluntary. There are various incentives for not reporting well, but ultimately it’s up to the facility to report it.

To get around these limitations, you used old manufacturing directories to create a new database of these hidden sites in four cities. What did you find out about where these sites end up locating over time?

SF: Size matters when thinking about the spatial geography of manufacturing in a given city. In every city we looked at, there are areas that have been identified and zoned for heavy industry. Those industrially zoned areas – historically, they’re usually in low-laying land along riverbanks, along rail lines and, more recently, along interstate highway exchanges – have been zoned for industry for a long time. And you have a very high density of legacy sites in those areas. These sites are usually what you think of when you think of heavy industry: they’re big factories of one sort or another that are visible in the landscapes. Today, they may look like an upscale loft apartment, but you can easily see from the exterior of those buildings that they used to be factories of one sort or another.

But what we also found is that, over time, there is a gradual but steady spread. So as sites accumulate, they also spread out. One reason for this is because sites that were industrialized in the past are actually infrequently replaced by other industrial activities.

You can imagine a parcel of land that has some old factory on it. In an ideal situation, when that factory closed down, another factory would go in right there on that same parcel of land, occupying that same building. But we found in our data that that’s not what commonly happens. What commonly happens is some other kind of activity takes that place, and the redevelopment involves something other than hazardous industrial activities.

The smaller manufacturing facilities – many of which are never recorded by regulatory agencies and are not bound by the zoning rules that corral the large factories – begin to increasingly pepper the landscape as they move around. These smaller facilities also turn at a faster rate than the larger facilities; they go in and out of business more frequently, and because they’re smaller, they’re easier to redevelop into other things ... they kind of disappear from the visible landscape more quickly.

An interesting, and somewhat surprising, consequence of all this change and churn is that it’s not just minority and low-income communities that are being exposed to these potentially hazardous sites.

JE: When we run the analyses on who is likely to be exposed through residential proximity, we do also find things that we’ve come to unfortunately expect from the vast research on environmental injustices. We do find that these larger facilities are opening up and disproportionately concentrating in areas of ethnic minority and low-income settlement.

But when we begin to consider the spread and the accumulation across cities as land uses change, that picture also changes. We begin to see, as one of our colleagues put it, that we’re all in this together. Many different types of neighborhoods are exposed.

You also looked at what kinds of hazardous sites do attract attention from regulators. What are the characteristics of sites that get cleaned up?

JE: We collected this historical data on thousands of sites, and then we matched the data from our database with local and federal data on those sites that have actually been inspected, or, in some cases, suspected of being contaminated but not yet inspected. When we match that and begin to predict the different qualities of facilities that do gather EPA attention and attention from the local department of environmental quality, it’s the sites that the risk containment process we talk about would predict, so it’s large facilities that have been in place for decades. It’s sites where people are most likely to be aware that there’s already been a problem because the facility has been operating on a large scale for a long time generating products and waste that are of high concern locally.

You highlight a few different recommendations that regulatory agencies could implement to better identify these hidden dangers. Can you talk about some of those?

SF: Regulatory agencies need to create roles for people to do the kind of historical work we’ve done to recover this lost knowledge about these legacy sites. The data is sitting in historical manufacturing directories on the shelves of state public libraries in virtually every state in the country, but I don’t know of any agency that actually does historical site investigation as a general practice.

Another, more general, recommendation is just the possibility of sustainable cities or sustainable succession. It’s critically important that urban planners and urban policy people who are talking about green cities and sustainable cities take history seriously. For me, that’s one of the main takeaways from this book: cities are historical processes, and you can’t just pretend that some new technology and a new transportation infrastructure is going to make everything OK.

We have to reckon with the long history of chemical and industrial production and chemical use in our societies; much of that legacy is buried all around us. To pretend it’s not there because it’s not visible is a real mistake.

This interview has been edited for length and clarity.