Dealing with Soil After Katrina:
A Focus on Arsenic

Photo Credit: Environmental Protection Agency

Immediately following Katrina, many of us found our yards covered with a thick layer of sediment left from the flood waters. Soil samples indicated arsenic was frequently found in that sediment at levels above the Environmental Protection Agency’s (EPA) screening level of 0.39 ppm. These findings raised concern in the public and the media. It is important to note that pre-Katrina, in Louisiana, the average background level for arsenic was 12 ppm. In New Orleans, background levels pre-Katrina were as high as 20 ppm. These background levels may be related to natural soil composition, past use of arsenic-based pesticides, pressure treated wood, trash incineration, and leachate from lead batteries for automobiles

THE BASICS

Arsenic is a naturally occurring steel grey, metal-like element in the earth’s crust. Inorganic arsenic is elemental arsenic combined with elements such as oxygen, chlorine, and sulfur. When elemental arsenic is combined with carbon and hydrogen it is referred to as organic arsenic. This differentiation is important as exposure to inorganic arsenic is often more harmful than organic arsenic. Unfortunately, most arsenic compounds are odorless and do not evaporate, therefore you can rarely tell if the compounds are present in your food or water.

Arsenic production has greatly decreased in the United States, but imports have increased steadily and substantially in recent years. In the US, organic arsenic often was produced as a byproduct of copper and iron smelting. If left unfiltered, this arsenic floated through the air as a fine dust and then settled in the surrounding areas.

Most arsenic currently used in the United States is in the form of copper chromated arsenic (CCA) in “pressure-treated” wood. In 2003, wood manufacturers completed a voluntary phase-out of using CCA in wood products for certain residential uses including picnic tables, recreation equipment, and decks. All outdoor wood structures, including wood fences built before 2003, still contain CCA and extra precautions need to be taken when disposing of this wood.

In certain parts of the state, arsenic levels in the soil may be related to past and current use of pesticides in cotton farming. Inorganic arsenic compounds are no longer allowable in agriculture, but organic arsenic compounds are principally used in cotton production.

HEALTH CONCERNS

There are multiple pathways (ways) through which we can be exposed to arsenic. Since arsenic is naturally found in the environment, we often are exposed to arsenic through the water we drink, food we eat, and air we breathe. For adults the main route of exposure is through the food we eat. Estimates indicate that are daily average intake for adults is 11 to 14 micrograms per day. This largely comes from meat, fish, seafood, and poultry. Fish arsenic has low toxicity to humans. Children are often at the greatest risk for higher exposure to arsenic because of their propensity to eat dirt. Our skin also may be exposed when water and soil contain arsenic.

Ingesting inorganic arsenic at high levels can increase the risk of lung, bladder, liver, kidney, prostate, and skin cancer and at high levels of ingestion even death (above 60,000 ppb). For this reason, the EPA has determined that inorganic arsenic should be considered carcinogenic to humans.

Inhalation of inorganic arsenic is another pathway of exposure. The most common health effect of high rates of inhalation exposure is a sore throat and irritated lungs. The exposure level that produces these effects is uncertain, but it is probably above 100 micrograms of arsenic per cubic meter (µg/m3) for a brief exposure. At low levels of exposure, both from inhalation and ingestion, the most common health effect is the darkening of the skin and the appearance of “warts” and “corns”.

WHAT DOES THIS MEAN FOR US?

So, what should our health concerns regarding arsenic be as we continue to move back into our houses and rebuild? Prior to Katrina, the New Orleans area had high levels of arsenic present in the soil due to both geology and human practices. This soil was under ground cover and concrete. Soil with high levels of arsenic may have slightly shifted due to the flood waters. Immediately following the storm the greatest health concern was that arsenic may be more bio-available (or able to absorbed by our bodies). This was of particular concern in neighborhoods where receding floodwaters left lawns covered with sediment and killed much of the grass and vegetation. Over the past year, much of the sediment has washed away and vegetation has returned to many of our yards.

If you are still concerned about  your family’s arsenic exposure, continue to try to keep young children from putting their hands in their mouths after they have been playing in dirt. If there are bare spots in your yard, attempt to grow grass and other ground cover. Sunflowers, brake ferns, and poplar trees also remove heavy metals such as arsenic from the soil. Many have also expressed worry about growing vegetables, Dan Gill offers his expert advice on gardening safety. This being said, there remain areas in the city that are “hot spots” with regard to arsenic levels, particularly in areas where pesticides were disposed of. in the past. In these areas, there needs to be on-going monitoring and a larger scale clean-up may be required.

References:

Agency for Toxic Substance and Disease Registry (ATSDR)
http://www.atsdr.cdc.gov/toxprofiles/phs2.html
Environmental Protection Agency (EPA)
http://www.atsdr.cdc.gov/toxprofiles/phs2.html

Louisiana Department of Environmental Quality (LA DEQ)
http://www.deq.louisiana.gov/portal/portals/0/news/pdf/arsenicexplainedjan10.pdf

Natural Resources Defense Council
http://www.nrdc.org/health/effects/katrinadata/sediment.asp

Links for More Information:

Arsenic and human health portal
http://www.sis.nlm.nih.gov/enviro/arsenicandhumanhealth.html

Arsenic basics from the National Library of Medicine
http://toxtown.nlm.nih.gov/text_version/chemical.php?name=arsenic

Association of Environmental Health of Soil

This is a state by state survey of how arsenic is regulated in the US.
http://www.aehs.com/surveys/arsenic.pdf

Louisiana Department of Environmental Quality (LA DEQ)
An explanation of arsenic data collected post Katrina.
http://www.deq.louisiana.gov/portal/portals/0/news/pdf/arsenicexplainedjan10.pdf

Natural Resources Defense Council
This page summarizes results for samples collected in October and November, 2005 by NRDC and other independent testers, as well as a limited number of EPA samples.
http://www.nrdc.org/health/effects/katrinadata/sediment.asp

United States Geological Survey (USGS)
This is a technical document describing backgound levels of 22 elements in soils throughout the US
http://pubs.usgs.gov/pp/p1648/p1648.pdf