How Coal Affects Water Quality: State of the Science

After a recent spill at a British Columbia marine coal export terminal, the general manager was quoted in a local newspaper saying:

There’s a lot of misinformation around coal. Coal is a naturally-occurring mineral. It is not toxic.

Leaving aside his non sequitur—plenty of naturally-occurring minerals are toxic—he’s right that coal is subject to a lot of misinformation. There is a lot we should know, but don’t, about coal. For example, we don’t know nearly enough about how coal and coal dust near terminals can alter freshwater and marine environments.

There’s no doubt that coal often contains a range of nasty pollutants, including uranium, thorium, arsenic, mercury, lead, and other elements that are toxic at low concentrations. But it’s also believed to be true that most of those substances do not enter the environment, at least not in large quantities, until the coal is mined, burned, or otherwise tampered with.

Despite the fact that the global coal trade moves somewhere in the range of a billion tons of coal on the oceans each year, there has been very little research into the effects of coal and coal dust on waterways and the ecosystems they support. As the Northwest considers adding as much as 140 million tons of coal export capacity on rivers and coasts that are home to sensitive and endangered species, it is a question that demands rigorous inquiry. What follows is our attempt to summarize the most germane findings from published scientific research.

In recent years, scientists have studied contamination resulting from a coal ship that sank in 1891 near Victoria, British Columbia. Studies in 2009 and 2012, for instance, indicated that the sunken vessel remains to this day a source of polycyclic aromatic hydrocarbons (PAHs) and other pollutants, but that their contribution is smaller and less harmful than Victoria’s (notoriously bad) sewage outfall and other man-made sources.

Other studies of PAH contamination from coal have been similarly inconclusive, mainly owing to a lack of adequate investigation. In a 2009 literature review, researchers at the University of Vienna observed that PAHs from unburnt coal may be an important source of aquatic contamination, but they concluded that the issue has “not been well studied” and that “the data is presently insufficient” to determine whether PAHs from coal pose a severe risk for humans or bottom-dwelling animals.

Apart from the presence of pollutants like PAHs in coal, the simple presence of coal dust has been shown to cause ecological harm. In South Africa, for example, a 2004 study found that coal dust from the Richards Bay Coal Terminal harms local mangrove trees and related ecosystems by impairing the ability of the trees to photosynthesize. The researchers noted:

…[coal] dust on the undersurface of leaves is not removed by wind, rain, or even physical washing. The undersurface of the leaves, as well as the rough surfaces of twigs, branches and trunk, tend to accumulate dust and appear black.

In 2006, here in the Northwest, Ryan Johnson and Marc Bustin of the University of British Columbia evaluated 22 years of coal dust dispersal around the Westshore Coal Terminal, located just north of the US border. They found widespread coal dust on the surface of the water near the terminal, observing a film of fine coal particles floating on the water 200 meters east of the vessel loading dock, even when no coal loading was in progress and no ship was docked. They pointed out that ordinary tidal currents could disperse the coal particles 2.5 miles from the coal loading facility, and potentially over 56 miles under extreme conditions.

On the sea floor, Johnson and Bustin were able to document a steady accretion of coal dust. They found that coal concentrations in marine sediments effectively doubled in the period covered by their analysis, increasing from a mean concentration of 1.8 percent in 1977 to 3.6 percent in 1999. Concentrations in the immediate area of the coal terminal were as high as 11.9 percent in the later samples, with quantifiable concentrations 1.5 miles away.

All of which, they conclude, could harm the flora and fauna living on the sea bottom. Oxidizing coal particles reduce the oxygen available for clams, mussels, barnacles, and crab larvae, with damage reverberating up the food chain. In fact, the bottom-dwelling invertebrates affected by coal dust make up a large share of the seasonal food for salmon and herring. (In fairness, however, the researchers also noted that low oxygen conditions deriving from coal dust would likely only occur within 300 meters of the terminal, and they claim that sea creatures in that area are more likely to be affected by physical changes to their environment, such as by dredging, than by oxygen depletion.)

More illustratively, Johnson and Bustin point out that some crabs from the Roberts Bank area, where the coal terminal is located, have been reported to have a “darker coal-coloration” and that local fisherman “find the darker color more difficult to market.” Presumably the darker coloration results from coal dust staining the shells of crab near the terminal or perhaps from adaptation to a darkening of the sea floor from coal dust deposits.

By far the most comprehensive scientific study of coal dust in the marine environment is Michael J. Ahrens and Donald J. Morrisey’s 2005 literature review of the risks of unburnt coal in the marine environment. Although they highlight the potential dangers of coal to the marine environment, they also emphasize how inadequately the issue has been studied:

…it was surprising that there was relatively little information on the bioavailability of contaminants from coal, or on the biological effects at the levels of organisms, populations or assemblages directly related to coal, either in the laboratory or field. This lack of information on the ecological effects of unburnt coal was unexpected in view of the common occurrence of coal in the marine environment…

Unexpected, and potentially problematic for regions like the Northwest that are considering very large expansions in coal infrastructure in sensitive aquatic areas.

Ahrens and Morrisey were able to identify several studies that examined the effects of coal dust pollution on fish and shellfish. Unfortunately, most of the studies are old, poorly designed, or inconclusive. For example, a 1963 study found that coal washery solids in relatively low concentrations reduced the growth rate of exposed trout. An even older study from the late 1930s linked fish mortality to the irritation caused by coal particles entering a freshwater stream. And a 1979 study by an EPA researcher found that to PAH contamination from coal reduced the spawning success of fathead minnows from 90 percent to 36 percent.

Perhaps most worrisome for the Northwest, a 1997 study by government researchers in Canada found that coal dust altered genetic expression in juvenile Chinook salmon. Although the consequences could be very serious, the study’s authors state that “the physiological consequences of this are presently unclear.” (In a concerning aside, the authors noted, based on earlier research, that “surfactants,” the chemical adhesives commonly used to reduce coal dust on trains, can boost the ability of coal pollutants to enter the environment, and the Washington State Department of Natural Resources raises similar concerns about surfactants.) We were not able to find any follow-up analysis; however, PAHs have been linked to growth impairment and reproductive effects on Chinook.

Also of particular interest to the Northwest, a 1977 study by the Canadian Fisheries and Marine Service (cited by Ahrens and Morrisey) apparently found coal particles accumulating in the gills of crabs near BC’s Westshore Coal Terminal, though the biological effect on the crabs was unclear. A 1981 study of Dungeness crab by the Canadian government found no measurable effect of coal particles after 21 days of exposure versus crabs in a clean tank, but Ahrens and Morrisey caution that the study was poorly designed. Again, we were not able to find any subsequent examination of crab populations.

A 1987 study of eastern oysters found no increased mortality after exposure to coal dust, but Ahrens and Morrissey note that the study may have included “major bias” owing to very high background levels of PAHs, which could have swamped the effects of PAH concentrations from coal particles in the experiment. Once again, we were unable to locate any further study of coal’s effect on shellfish, though subsequent studies have found that PAHs affect the growth of mussels.

So there is reason to be concerned that pollution from unburnt coal can harm fish and shellfish. Unfortunately, the subject is marked most prominently by a lack of recent scientific examination. As Ahrens and Morrissey point out, however, coal may pose a less severe chemical hazard in the marine environment than a physical one. They note that coal has “well documented” physical effects similar to other suspended or deposited sediments. It abrades, smothers, dims light, and clogs both breathing and feeding organs. They also observe that, “it is often difficult, if not impossible, to separate toxic effects from physically induced stress.”

Suspended solids are problematic because they can kill the eggs and larvae of fish and invertebrates on the sea floor (though research to this effect has not been conducted specifically with suspended coal.) For example, a 1998 study in Southeast Asia showed that accumulating silt reduces the number and diversity of species in sea grass ecosystems. Ahrens and Morrisey assume that the deposition of fine coal particulates would have similar effects. Plus, reduced water clarity from sediments can make it harder for visual predators like fish to find food, according to a 2001 study. Just so, a 1995 study of coal waste dumped off the coast of England (where coal particle contamination was similar to that near BC’s Westshore terminal) found a reduction in the number and diversity of marine creatures.

Most scientific studies appear to find that the major threat posed by coal dust to water bodies may be physical, not from toxins in the water. Ahrens and Morrissey, however, emphasize that the issue has not been examined carefully, and there is some solid scientific basis for concern about chemical pollution deriving from coal. For example, one study in Canada found that coal in the water can be a source of acidity, salinity, trace metals, hydrocarbons, chemical oxygen demand and, potentially, macronutrients. In fact, Washington’s Department of Natural Resources says that materials in coal can react with seawater to produce “localized ocean acidification.” All of these factors pose potential hazards to aquatic organisms, such as by increasing the risk of invasive species taking hold, as a 1996 study found.

In 1978, US EPA researchers believed that runoff concentrations from the coal piles they evaluated were far below thresholds that would stress aquatic organisms. Yet Ahrens and Morrissey found in their 2005 review that acidic runoff from coal piles is a common problem with storage and handling facilities, particularly with high sulfur coal. In freshwater streams, coal runoff can contribute to reduced diversity of aquatic creatures, according to a 1985 study in Maryland, and reduced numbers of them, according to a 1980 study in Wales.

Moreover, Ahrens and Morrissey point out that the mineral salts in coal oxidize in water, which means that coal pile runoff may also harm aquatic organisms by raising salinity levels in freshwater environments. (Increased salinity is, of course, less problematic in marine settings because seawater is naturally salty.)

Coal can also increase the level of macronutrients, particularly nitrogen and phosphorus. Most nitrogen in coal is released only upon heating, but Ahrens and Morrisey point out that the issue has not been well studied. A 1996 study of Spanish coals found that “little phosphorus was mobilised by water.” On the other hand, a 2002 study of Australian coals found that 60 percent of the phosphorus content could leach into the surrounding environment.

While ash from burning coal can be dangerously radioactive, Ahrens and Morrissey conclude that the radioactive elements in unburnt coal, including uranium and thorium and other isotopes, do not likely pose an environmental threat. This is apparently because radioactive elements in coal are generally of a similar order of magnitude as that in soil or shale.

At the same time, coal can release heavy metals, though the risk varies greatly by the type and purity of the coal. Yet Ahrens and Morrisey found that for nearly every metal analyzed, there was a coal leachate that exceeded international water quality guidelines. For example, some metals in leachate samples from low-sulfur western US coals exceeded the Canadian water quality guidelines for protecting aquatic life. In a 2004 study in Israel, researchers found that snails in the Mediterranean near an Israeli power plant were harmed by the presence of coal in the water, perhaps owing to elevated levels of cadmium.

The Northwest is considering building new export terminals that could ship as much coal as the rest of the United State combined. Yet the region is in the dark when it comes to understanding the risks of coal on sensitive ecosystems and endangered species. Scientific studies raise a variety of concerns, but the most comprehensive reviews also suggest that the core issues have not been well-studied and that the aquatic risks of coal are poorly understood.

It seems critical to us that the region thoroughly study the potential hazards—both chemical and physical—of large-scale coal shipments to aquatic systems. That means Northwest decision-makers should demand robust scientific inquiry into the risks of coal-based pollution in the Salish Sea and Columbia River, where the coal industry has proposed to locate operations.

David Kershner, a Sightline fellow, lives on one of the San Juan Islands.