Pesticides and Sediment Types in Tecolote Canyon

Little did we know but March was adventure time for our lab.  Groups trekked through trees, hedges, rocks and dirt across the trails of Tecolote Canyon.  We braved the sunny hike, ever alert of the possibility poison oak could threaten around the next bend.  Our goal?  Collect dirt to test for presence of the pesticide chlordane.  

some of the sites explored approximated by red dashed lines

Chlordane is a pesticide with a rather complicated looking structure (pictured at right).  For about forty years, from 1948 to 1988, chlordane was widely used until it was limited to termite fumigation.  Its use was halted because chlordane is like gum stuck on the bottom of your shoe - hard to get rid of once it's around.  It persists in the environment, which is not a good thing especially if there are worries that at high levels the chemical can harm human health.

In addition to chlordane hunting, we tested our dirt to find out some more information about their "personality types" - like how much water they had and how sandy they were.  For example, when you take a closer look at dirt you will notice its basically a bunch of tiny beads, or particles.  The composition and therefore how "sandy" a dirt sample is varies, depending on the amount of different sizes of these particles present.  The types we focused on were sand, silt and clay.  Basically, sand is the biggest while clay is the smallest in size (illustration is for comparisons, not actual size).

We did some tests on our dirt for chlordane; yes, they involved some color changes (yay!).  We compared those results to the characteristics of each dirt sample.  It was important for us to analyze the dirt in order to get an idea how good it would be at letting stuff (like pesticides and other contaminants) stick to it.  

In the end, one trend that appeared to pop up was that the more silt and clay a dirt sample had, the higher the chlordane concentration relative to the other samples.  Further, the concentration of chlordane in Tecolote Canyon has increased slightly from the 2005 levels past environmental chemistry found (there was a decreasing trend but that was reversed sometime after 2010).  What these results tell us is that (1) finer dirt (as opposed to rougher, sandier dirt) seems like a better magnet for the chlordane pesticide; and (2) chlordane sure does take a long time to get rid of, no exaggeration.  

Something else I learned was how big Tecolote Canyon is.  I was convinced it was limited to the stretch of scratchy wilderness behind USD; and wow was I wrong!