For the past three years, we have been working with students from North Central High School on our Fungi Project. We began our innovative Fungi Project to investigate the ability of several species of mushrooms to break down persistent polychlorinated biphenyls (PCBs). This project aims to prevent PCBs from entering our urban waterways and making their way into the food and water supply.
Working with two students, Alyssa and Sanda, and teacher, Dan Shay, we recently received the bioremediation results from Les Stephens, a retired bioremediation expert. Here is what he found:
There was a reduction in PCB levels from initial 1400 parts per billion (ug/Kg) to 750 ppb (46% reduction). On the Total Petroleum Hydrocarbons analysis, the Diesel Range Organics reduced from 760 parts per million (mg/Kg) to 170 ppm (78% reduction) and Residual Range Organics reduced from 4000 parts per million to 1500 parts per million (63%).
There is good bioremediation of the City's contaminated soils! In addition, their genetic study showed that the composition and diversity of the microbial population changes dramatically with time as biodegradation proceeds with increasing populations of known bacterial remediators. This will be an exciting area of inquiry for the team to explore going forward.
Quick notes: only one congener Aroclor 1254 is present in lab tests. PCB congeners are a mixture of compounds and 1254 refers to the 12 carbon atoms bonded in the two joined benzene rings and the 54 means 54% chlorine is present in the mixture. Not all carbon atoms are bonded to chlorine atoms, and can be bonded to a hydrogen or another carbon atom instead. The chlorine-carbon bond is a strong chemical bond along with the double carbon bonds in the benzene rings making these chemicals extremely persistent in the environment with the potential to bioaccumulate in animals. The fact that we have biodegraded PCBs using native soil populations of bacteria and fungi with amendments is exciting and important work.
PCBs are a class of chemical compounds in which chlorine atoms replace some or all of the hydrogen atoms on a biphenyl molecule. The general chemical structure of chlorinated biphenyls is shown below:
