Why are there high levels of arsenic in some Acadiana soils?

Figure 1. "4 Sources of Arsenic You’d Never Expect"

Introduction - The issue of arsenic contamination may at first appear to fall outside the scope of I-49 Connector (The Con) questions. However, arsenic contamination of our soils is an issue that does intersect with The Con's issues. In this post I will give some background about how elevated arsenic came to be in our parish soil, how it can impact us, and what we need to do about it.

If you recall the periodic table from your school days, arsenic is chemical element number 33 with the symbol As. Arsenic falls in the table just below phosphorus in column 15, and this means that arsenic may react in ways that are similar to phosphorus and disrupt some chemical reactions that are essential to life.

Sources of arsenic contamination - Arsenic was used for many purposes in the past, but is much less widely used today. In the southern US, arsenic pesticides in the form of lead arsenate dust and other formulations were regularly used on cotton crops to control boll weevils prior to the development of organic pesticides like DDT in the middle of the 20th century (Figure 2).

Figure 2.  Dusting cotton from"A is for arsenic" Wired 6/19/2012

Figure 3. "Arsenic and Old Railyards" F. Harrison

Along side sugar cane and livestock, cultivation of cotton provided an economically important income for Lafayette farmers since the earliest days of our town then named Vermilionville (Griffin, 1959).  Cotton farming has now come to an end in Lafayette Parish (Soil Survey of Lafayette Parish, LA, 1916; Soil Survey of Lafayette Parish, LA, 1977; NRCS Web Soil Survey, 2017), but in many places the legacy of arsenic pesticide use remains in our soil. Today in Acadiana, many sugar cane and rice fields cover the ground where cotton once grew, and the legacy of arsenic contaminates our rice crops (C. Poterra, 2007; B. Goodman, 2011;  T. Greenaway, 2012; Consumer Reports, 2012). Recent spreading of suburban development on our former cotton fields may also lead to routine but unrecognized exposure of Acadiana families to arsenic.

Arsenic was also used routinely in railroad operations to preserve rail ties and other wood, and to kill weeds along the right-of-way (MADEP, undated) so that engineers had an unobstructed view ahead and along each side of the tracks. Planned "rails-to-trails" projects have been complicated or even blocked by by the discovery of elevated soil arsenic levels leading to unanticipated clean-up costs (Ciabotti et al, 2004). The Rails-to-Trails Conservancy has published a compilation of case studies and guidance related to understanding contamination issues (Ciabatti et al, 2004), and the State of Massachusetts has recognized that repurposing of abandoned railroad routes poses a risk, and have published guidance in the form of Best Management Practices (BMPs) for the development of rail-trails (Massachusetts DEP, undated).

The railroad was completed to Vermilionville in 1880, and today continues to run through our city which is now named Lafayette. The arrival of the railroad connecting New Orleans and Houston brought jobs, growth, prosperity, and commerce to our city. Steam trains which burned bunker oil had limited range, and all trains passing through Lafayette had to stop for refueling and to take on water and sand. The Lafayette railyard grew to be a major facility employing up to 1000 workers and providing complete maintenance service for the early steam engines (Griffin, 1959). There is now concern that the downtown railyard which was abandoned in the mid 1960s (Louisiana DOTD Draft Phase I ESA, 2016) will contaminate the Chicot Aquifer and our municipal water wells (C. Taylor, 2016).

Arsenic contamination of old railyards and rail lines has been found across the US. The abandoned Union Pacific Railroad Ashland site in Oregon is likely typical (Harrison, 2008). This railyard has similarities in age and past uses to the abandoned Lafayette yard, but the Ashland site is roughly half its size and poses little risk to water supply wells or local groundwater below the surficial level. The UPRR-Ashland site operated as a locomotive maintenance and refueling station from 1887 until 1986. Also, in contrast to Lafayette, the UPRR is actively working to remediate the Ashland site.

Figure x. Cultural Thoughts

Health impacts of arsenic - Despite the fact that arsenic has been used as a poison for centuries, the more subtle chronic health impacts from long-term exposure were often not recognized in the past, to the extent that low doses of arsenic were often used as a medicine or tonic (Wikipedia-Arsenic Poisoning History). It is now recognized that chronic exposure to arsenic can cause many ailments including thickening of the skin, darker skin, abdominal pain, diarrhea, heart disease, numbness, stroke, diabetes, chronic respiratory disease, and cancers of the skin, lung liver, and kidney. There is no evidence based treatment for chronic exposure; therefore, management must be focused on reducing exposure (Ratnaike, 2003).

Arsenic standards, levels, and limits - The USEPA sets standards for allowable concentration of contaminants in drinking water. These are called Maximum Contaminant Levels or simply MCLs. In setting an MCL, EPA first determines what concentration of contaminant would cause no health effect, and terms this concentration the Maximum Contaminant Level Goal or MCLG. In setting the MCL, EPA considers the cost and practicality of treatment weighed against the public health risk for the specific contaminant. The MCLG for arsenic is zero, meaning that there is no minimum concentration below which there is no health risk. In 2000, the EPA initially proposed an MCL of 5 ug/L (micrograms of AS per liter), but considered other levels of 3, 5, 10, and 20. After comments were received and reviewed, the final and current MCL for arsenic was set at 10 ug/L with an MCLG of zero.

In the US, public water suppliers are required to test for arsenic and meet standards after treatment. However, many private wells may be untested and can be a significant risk to adults and especially to children. The short 10-minute film In Small Doses: Arsenic gives useful background information on the risks from arsenic and discusses the risk of arsenic exposure from private wells in New England.

Beyond the concern for exposure to arsenic through rice which was mentioned above, other foods can be a pathway for exposure and risk. A 2012 study by Consumer Reports provides much useful information. The FDA does not currently regulate the amount of arsenic that can be present in our food. However, Dartmouth University's Children's Health web site recommends that we should: (1) limit rice consumption, choose white rather than brown rice (2) limit apple juice consumption, drink other juices, or skip drinking fruit juice (3) read labels because rice sweetener in the form of brown rice syrup is used in many foods. Dartmouth also recommended always rinsing rice before cooking, but recent research reported by the FDA shows that rinsing rice before cooking results in very little arsenic reduction, but does reduce some valuable nutrients. Gardening on arsenic contaminated soil can present concerns. The Washington State Cooperative Extension has published guidelines for gardening on lead and contaminated soils (F. Peryea, 1999). One simple recommendation is to carefully wash garden fruits and vegetables to remove all traces of soil before eating.

In addition to arsenic exposure from food and drinking water, exposure from breathing contaminated air must be limited. For employees, OSHA sets exposure limits based on an 8-hour average concentration of arsenic in air. OSHA sets the arsenic action level at 5 micrograms of AS per cubic meter of air. Personnel working on the abandoned railyard property and along the rail line should take care to limit their exposure to contaminated soil and dust. Lawn mowing and weed control, for example, may produce dust contaminated with arsenic and other soil contaminants. And, it follows that the public needs to be assured that they are protected from dust blowing from these sites through careful management of all activities on the sites which may create dust leaving the property boundaries.