Toxic chemicals are poisoning our rivers, oceans and soil, causing cancer and even polluting human breast milk. Could waste-eating bacteria be the solution? He Jianzhong is an Associate Professor in the Department of Civil and Environmental Engineering at the National University of Singapore. For our XxXX series on ten inspiring women in science and technology, she talked to us about touring the world's most polluted sites in search of the ideal bacteria, and finding powerful little cleaners.
What do you do?
I use micro-organisms to detoxify pollutants in the water or soil. These pollutants can cause serious health problems, but we've discovered a special group of bacteria that can break them down and clean up our environment.
Why is this better than conventional ways of treating waste?
Right now we don't have very good technology to detoxify a big group of industrial pollutants, what we call persistent organic pollutants. They can cause cancer, disrupt the hormone system and cause reproductive problems. The existing processes are very expensive or energy-intensive, and some can produce secondary contamination. Our bacteria are already available in the environment. We just have to find them, understand them, then apply them.
What are these persistent pollutants, and how common are they?
One group are the polybrominated diphenyl ethers (PBDEs). It's a common flame retardant that's found in furniture, paint and electrical goods, like computers or refrigerators. The compounds are hydrophobic, which means they don't like water, but they love to dissolve in human tissue, because there is fat in tissue. Humans ingest them through the food chain, but as it's very hard for our body to discharge them, they accumulate and cause cancer or destroy the hormone balance. Since the 1970s, the presence of PBDEs in our bodies and in our environment has been increasing exponentially. A high concentration of PBDEs has been found in human breast milk. They've even been found in polar bears in the Arctic, a region we always assumed was clean. They were probably introduced there by fish migrating from polluted rivers.
Many manufacturers in the US and Europe have voluntarily stopped using PBDEs. But they are in so many existing household products, and when we throw them away, they enter the food chain.
So how does your bacterial detox work?
Our bacteria feed on pollutants. They remove bromine or chlorine from the compounds - that's the part that causes cancer, or disrupts the hormone system. What's left behind is safer or even has no toxicity at all. The tough part is removing it. After that, the compound is easily degraded. This process is known as bioremediation.
Is this already being used?
Yes! One company in the US is using two of our bacteria to clean up organic solvents. The US Environmental Protection Agency is going to use bacteria from our lab on a large scale to clean up 1,300 contaminated sites, where our bacteria can play a great role. Right now, we are looking for companies in China and Malaysia to apply our bacteria there.
What's your biggest challenge?
Our bacteria are already present in heavily contaminated sites, but in small quantities. We might screen a hundred sites in the US, China, Malaysia, Singapore and Indonesia, and maybe only find one or two sites with these promising bacteria. In the United States, we've found them in Michigan State, and in the Hudson River in the New York area. In China, we've found them in Guangdong Province. We now have more than a dozen very good micro-organisms in the lab.
Our next challenge is to understand what makes the bacteria thrive, so we can apply them to the sites. Which supporting nutrients, such as vitamins, can make these bacteria grow better and speed up bioremediation?
How fast is the process right now?
Our bacteria can remove bromine or chlorine from the compound within two weeks. It used to take more than a year to remove just 10% of that. Maybe our bacteria evolved to degrade these compounds, because they lived in such heavily polluted sites. That's another aspect we're studying, which functional genes play a part in this process.
Instead of developing these high-tech solutions, can we not just ban pollutants?
Compounds like PBDEs are very stable. That's what makes them so hard to degrade, but it's also what makes them very useful as flame-retardants, for example. If they weren't stable, they'd burn. Right now, it seems that we cannot produce a similarly stable compound that's not toxic. If we replace PBDEs with another chemical, it may seem non-toxic now, but that's what we initially thought about PBDEs, too. So should we really switch to another compound, for which we don't have a solution yet? Is it perhaps better to use PBDEs, which we already understand, and detoxify them before discharging them into the environment? These are open questions.
You are a successful female scientist and innovator. What’s the one thing we as a society could do to attract more women to the STEM fields?
In my field of environmental engineering, most researchers are male. But women can do this work just as well. They are very good at research, very careful. I think there are two things we could do to encourage them to come into this area. One would be to offer a scholarship for women postgraduate students. Another would be to support female researchers with families. Our tenure clock is very tight, either you get tenure within five to six years, or you are kicked out. If we could give women more time, because they also need time to take care of their families, that would probably help.
Interview by Sophie Hardach
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