According to the U.S. Geological Survey, bioremediation is a highly effective way of mitigating contaminants in soil: "Studies by the U.S. Geological Survey (USGS) had shown that microorganisms naturally present in the soils... actively consume fuel-derived toxic compounds and transform them into harmless carbon dioxide. Furthermore, these studies had shown that the rate of these biotransformations could be greatly increased by the addition of nutrients. By 'stimulating' the natural microbial community through nutrient addition, it was theoretically possible to increase rates of biodegradation and thereby shield the residential area from further contamination."

Cornell University: "Bioremediation provides a technique for cleaning up pollution by enhancing the same biodegradation processes that occur in nature. Depending on the site and its contaminants, bioremediation may be safer and less expensive than alternative solutions such as incineration or landfilling of the contaminated materials. It also has the advantage of treating the contamination in place so that large quantities of soil, sediment, or water do not have to be dug up or pumped out of the ground for treatment."

COMPOST

Compost is nutrient-rich fertilizer made from organic materials that have decomposed under certain conditions. The organic materials that constitute the ingredients of compost include food scraps, cotton, wool, burlap, woody materials, paper products, yard trimmings, and by-products such as blood, hair, and herbivore manure. These materials are then aided in decomposition by adding water and oxygen, and often worms and other invertebrates. According to the Rodale Book of Composting, "compost improves soil texture and structure, qualities that enable soil to retain nutrients, moisture, and air for the support of healthy crops. Compost helps control erosion that otherwise would wash topsoil into waterways. Compost is the best recycler of biological wastes, turning millions of tons of our refuse into a food-growing asset. Compost provides and releases plant nutrients, protects against drought, controls pH, supports essential bacteria, feeds helpful earthworms, stops nutrient loss through leeching, acts as a buffer against toxins in the soil, controls weeds, and conserves a nation's nonrenewable energy resources."

WORM COMPOST TEA

Compost tea is a liquid solution made by extracting beneficial microbes from compost and/or worm castings. In worm composting (also known as "vermiculture"), red worms consume bacteria, fungi, protozoa, and microarthropods which feed on compost to generate a highly concentrated compost called worm castings. The tea is then made by adding the compost and/or castings to aerated water and unsulfered molasses; it is brewed for several days in a process not unlike brewing hot tea. The resulting liquid is then sprayed onto soil. The benefits include direct nutrition: a source of foliar (leaf) and soil organic nutrients and micronutrients for easy plant absorption. There are also microbial benefits that occur in the soil itself: compost tea combats disease-causing microbes, degrades toxic materials, produces plant growth hormones, mineralizes available nutrients in the soil, fixes nitrogen, and prevents pathogens from infecting plants.

SUNFLOWERS

According to the Northern Virginia Soil and Water Conservation District, "phytoremediation is the use of specialized plants to clean up polluted soil. While most plants exposed to high levels of soil toxins will be injured or die, scientists have discovered that certain plants are resistant, and an even smaller group actually thrive. The thriving plants show a particular potential for remediation because it has been shown that some of them actually transport and accumulate extremely high levels of soil pollutants within their bodies. They are therefore aptly named hyper-accumulators.

"Hyper-accumulators already are being used throughout the country to help clean up heavy metal polluted soil. Heavy metals are some of the most stubborn soil pollutants. They can bond very tightly to soil particles, and they cannot be broken down by microbial processes. Most heavy metals are also essential plant nutrients, so plants have the ability to take up the metals and transport them throughout their bodies. However, on polluted soil, the levels of heavy metals are often hundreds of times greater than normal, and this overexposure is toxic to the vast majority of plants. Hyper-accumulators, on the other hand, actually prefer these high concentrations. Essentially, hyper-accumulators are acting as natural vacuum cleaners, sucking pollutants out of the soil and depositing them in their above ground leaves and shoots. Removing the metals is as simple as pruning or cutting the hyper-accumulators above ground mass, not excavating tons of soil."

Although sunflowers are one such hyper-accumulator, Replant New Orleans has been focusing energy on bioremediation, and are no longer conducting phytoremediation projects. If you would like more information about bioremediation or phytoremediation, please e-mail us your questions at trees@replantneworleans.org.