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Biogeochemistry

Sticking to it – Sediments act as a “sink” for pollution

 

 

Pozo, K., Urrutia, R., Mariottini, M., Rudolph, A., Banguera, J., Pozo, K., Parra, O., Focardi, S. Levels of Persistent Organic Pollutants (POPs) in sediments from Lenga Estuary, central Chile. Mar. Poll. Bull. 2014; 79: 338-341. doi: 10.1016/j.marpolbul.2013.11.031.

Background

Polychlorinated biphenyls (PCBs) were widely produced from the 1930s until their production was banned in the United States in 1979 after it was realized that PCBs are highly toxic.  There are 209 different “congeners” of PCBs, which basically means that PCBs can be found with varying numbers and positions of chlorine atoms on the same carbon backbone.  They are flame retardant, chemically stable, and have electrical insulating properties, and for this reason they were widely used in various industrial applications including, but not limited to: electrical transformers, hydraulic equipment, and in thermal insulation material.  Even once their toxicity was realized and their production largely banned, the problem was not entirely solved: Due to their persistence, PCBs are still found at measurable concentrations worldwide 40 years later.

PCB Congener Image

Example of a PCB congener. Image courtesy of Google.

Hexachlorobenzene (HCB) is another POP of similar nature except HCB’s primary usage was as a fungicide for crops until the US banned it in 1965.  HCB is also formed as an industrial byproduct.  Both PCBs and HCB are included on the original “dirty dozen” list of the Stockholm Convention (2001) and can be considered “legacy POPs.”  It is important to note that while the United States banned production of these chemicals circa 1970, many other countries took much longer to ban or phase out their use, and many are still used today.

One of the signature characteristics of a lot of POPs is that they are hydrophobic, or hate the water and would much rather be in anything fatty or high in organic content.  A chemical’s Koc is what’s called a partitioning coefficient, but don’t get scared away – basically the Koc is just a numerical value that tells you a little about the compound you’re looking at and how it’s going to behave in the environment. Specifically, the Koc tells you how strongly a compound will sorb, or stick, to sediment (in simple terms, ‘soil’ that lies underwater) that’s rich in organic content (e.g. a ‘mucky’ wetland sediment).  PCBs and HCB both have high Koc values, meaning they will sorb to sediment (with varying strengths depending on the “congener”) and will likely stay there, accumulating over time and thus making the sediment a “sink” for the pollutants.

Chile is a party to the Stockholm Convention after having signed on in 2003 and ratifying it in 2005, but there is still a lack of regulation of chemical residues in coastal regions of the country.  Around the time they signed on to the Stockholm Convention, Chile began to assess its inventories of certain pollutants, finding quite a high supply of some troublesome contaminants in materials that were recently or currently used in the region.  For example, in 2004, it was found that there was 324,641 L of dielectric oil containing PCBs in use; in between 2002 and 2008, around 38,820 metric tons of potentially-PCB-containing products were imported to the country; and HCB was being unintentionally produced as a an industrial byproduct. The Lenga Estuary, where this study took place, is a small coastal wetland in central Chile and while the estuary itself is located in the protected Hualpen Nature Sanctuary, the adjacent areas have undergone heavy industrialization and economic development, which has led to a higher contaminant load to the sediments in the region

This Study

Sediments were collected from 9 stations within the Lenga Estuary in July of 2002 and extracted for PCBs, HCB, and % organic carbon content.  It was found that some of the PCB levels found were extremely high (~20 to 10,000 ng/g dry weight) when compared to other regions of the world, which the researchers attribute to the extremely close proximity of industry to the study area.  HCB concentrations ranged from 1 to 870 ng/g dry weight, which means this compound is still present even though the country does not directly import, market, or manufacture it.  In addition, positive correlations were found between % organic carbon content of the sediment and both PCBs and HCB.  This was expected based on the compounds’ high Koc values, and this relationship further proves that % organic carbon content is a good indicator of how much contaminant adsorption can be expected.

Pozo et al. - Lenga Estuary POPs sampling site

Significance

This data contributes to research on pollution in Chilean coastal regions and helps to demonstrate the impact of industrial regions on nearby coastal areas that are important for maintaining healthy ecosystems.  PCB levels were extremely high and even HCB levels were considerable, likely due to its inadvertent production as an impurity in the currently used pesticide pentachlorophenol (PCP).  The authors address the fact that even though Chile is a party to the Stockholm Convention, there is a large lack of legislation with regard to pollution impacts on water quality and estuarine environments.  The high concentrations they found show that there is clearly a problem and hopefully this study and others like it will help encourage improvements in the region.

Discussion

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  1. […] but later stick onto or absorb into these aerosol particles and accumulate there, much like they stick to sediments and sink to the seafloor. When the aerosol is deposited in the water, it brings pollutants along with it. Scientists have […]

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