SHEILAH KAST, host:
In Harbin, in far northeastern China, the city's water supply was restored today according to the official Xinhua news agency five days after a shutdown due to contamination by benzene and nitrobenzene in the Songhua River. About 100 tons of the chemicals had spilled into the river following an explosion at a petrol chemical plant more than 200 miles upstream from Harbin. Rolf Halden is assistant professor of environmental health sciences at the Johns Hopkins School of Public Health and is co-founder of the school's Center for Water and Health. We spoke with him earlier this weekend and asked him about the characteristics of benzene and nitrobenzene.
Mr. ROLF HALDEN (Assistant Professor, Environmental Health Sciences, Johns Hopkins School of Public Health): They are similar chemicals. Benzene is a compound you can find in gasoline, and nitrobenzene has an additional nitro group to it but they're structurally related. These chemicals are volatile, so they are lighter than water. And at least benzene is contained in gasoline to a significant degree.
KAST: What does exposure to these chemicals do to humans?
Mr. HALDEN: Well, we can distinguish between short-term and long-term effects. Short-term effect exposure to benzene include temporary nervous system disorders. This could be drowsiness, dizziness, headaches or nausea or even loss of coordination, confusion and unconsciousness. There could also be temporary immune system suppression and possibly anemia. Long-term effects are chromosome aberrations which is essentially a damage of genetic information that can lead to cancer. So, for example, leukemia is known to be linked to benzene exposure.
KAST: Well, would this situation in China be a short-term or long-term exposure?
Mr. HALDEN: Well, it was a catastrophe in that there was an accidental release of a large amount of chemicals. These chemicals will over time attenuate. And so if people get exposed, it most likely will be a short-term exposure. People already have been exposed. It's very important right now to cut off the source from the receptors to protect people from getting exposed to the benzene at this point in time. Over time, in a few weeks, the chemicals will attenuate in the environment, so they will go away or break down and so the threat level will go down over time.
KAST: Well, much of the spill went into the Songhua River. Do benzene and nitrobenzene behave differently in water than in the atmosphere?
Mr. HALDEN: Yeah. They're different chemicals, so you can expect them to behave somewhat differently. Both chemicals will photolyze and then these chemicals can be biodegraded by microorganisms that are naturally present in the water.
KAST: And that happens whether they're in the air or in the water?
Mr. HALDEN: Well, when they're in the air, they will photo degrade. So light will do the damage and break down the chemicals. When they are contained in the water, when they are dissolved, then microorganisms can use them as a food source.
KAST: And parts of the river are frozen. So if the chemicals are trapped in ice, do they linger?
Mr. HALDEN: Yeah. Typically. So when we look at these chemicals, we don't consider them very persistent. So we expect them to break down fairly rapidly. However, the conditions are somewhat unfavorable right now in that it's very cold in the region and this will limit the amount of chemicals that will evaporate from the water and it will also slow down any biological processes and chemical processes that are contributing to the degradation of the chemicals. So the cold weather really is unfavorable, and in addition, if you have an ice cover on the river, than light cannot as easily get into the water and obviously it cuts off any volatilization of the chemical into the air from the water.
KAST: And the Songhua River flows north into far eastern Russia and ultimately to the Sea of Okhotsk. Are there threats that the benzene and nitrobenzene will stay a problem there?
Mr. HALDEN: Yeah, it will depend on how fast they degrade. Again, the temperatures are a little worrisome. If it was warmer, if this had happened in the summer, then the risk would be less. I believe that it is likely that these chemicals will be detectable when they reach Russia, which is a long trip. It's about 340 miles, I understand, downstream from Hardin. And there also is a confluence with another river, the Along Jung River(ph), in China which should help to dilute any dissolved benzene and nitrobenzene. But these chemicals certainly will be detectable at some level, and Russia should take some precautions with respect to using this water as a source of drinking water. But I expect that these chemicals will, in China, be detectable for quite some time.
KAST: Rolf Halden is assistant professor of environmental health sciences at the Johns Hopkins School of Public Health and co-founder of the school's Center for Water and Health. He joined us from his home in Baltimore.
Thanks for speaking with us.
Mr. HALDEN: You're welcome.
KAST: It's 18 minutes past the hour. Transcript provided by NPR, Copyright NPR.
