Seaweed has been shown to accelerate the breakdown of DDT in soil
‘"It was a eureka moment," he said, "when one morning I stood ankle-deep in seaweed and realized here's a substance that's got the right combination of elements" to work in DDT bioremediation -- cleaning up pollutants by biological means.’
-Ravi Naidu in The Washington Post Nov. 8, 2004 (Cheryl Lyn Dybas reporting)
DDT soil contamination is a major problem throughout the world and with the potential for ecosystem-wide and human health effects. DDT is a fat-soluble molecule, which presents two major problems: it tends to bioaccumulate in the food chain, and it is extremely persistent in the soil, because low solubility makes it less available to be broken down by microbes.
However, increasing dissolved organic carbon (DOC) in the soil can increase the bioavailability of DDT for degradation by microbes. Increasing DOC is thought to enhance microbe growth and metabolism. Sodium ions increase the DOC levels in soils as well as disperse the clay soil particles that bind DDT, thus making DDT more available for bioremediation. Researchers have found that sodium application enhances DDT transformation in contaminated soils.
This is why bioremediation of DDT soils is greatly enhanced by the addition of seaweed, a good source of both sodium ions and DOC, as well as Nitrogen, a limiting nutrient for bacteria growth. However seaweed is also a source of dissolved humic acid, which has been shown to decrease the biodegradation rate of DDT. The challenge for scientists, as is often the case in developing bioremediation technologies, was to determine the appropriate level of seaweed to add so that the biodegradation would be accelerated.
An additional consideration is that the biodegradation of DDT by microbes under aerobic conditions leads to the formation of DDE, a more persistent compound than DDT. Under anaerobic conditions, DDD is the metabolite formed, which is far less persistent. Therefore the first step in the bioremediation strategy for DDT contaminated soils should be flooding, to create anaerobic conditions. After that, experimentation can determine the optimum amount of seaweed to add. Too high levels of seaweed addition can actually inhibit DDT degradation, so care should be taken to determine the appropriate level for the soil conditions before attempting this strategy.
Sources: Kantachote, May 2004 and Kantachote, June 2004
Magic Mushrooms: White rot fungi cleans PCP contaminated soil
"It's a bit like making bread," Dr Farrell said. "First you get your starter for four weeks, then you mix with soil - roughly one part wood chips to nine parts soil. You make that into a mound, like earth composting, and let the fungus and the fungal enzymes work on the PCPs and dioxins."
-Roberta Farrell in The New Zealand Herald Nov. 10, 2003 (Simon Collins reporting)
Pentachlorophenyl (PCP) was traditionally widely used as a wood preservative, however its use has been largely discontinued due to its toxicity and persistence as an environmental contaminant.
White rot fungi has been shown to completely mineralize PCP to carbon dioxide. However, less than 1% of fungal strains tested survived PCP concentrations greater than 200ppb. Bioengineering PCP tolerant strains of fungi will be essential for bioremediation technology success. Other important factors to consider are that fungal survival is dependent soil type, pH, moisture content, and organic matter content.
White rot fungi is so successful at degrading xenobiotics because it produces extracellular oxidative enzymes that indiscriminately degrade aromatic molecules (i.e. lignin, as well as contaminants PCP, polycyclic aromatic hydrocarbons, and azo dyes). The oxidative enzymes cause one electron oxidation of the aromatics compounds and then further oxidation of the resulting radicals proceeds in the presence of oxygen gas until the compound is eventually mineralized completely.
A New Zealand based bioremediation company BioRemedi already has over 2000 tons of PCP contaminated soil under treatment using white rot fungi.
Sources:
PCP degredation using New Zealand white rot fungi
White rot fungi website (Jim Field)