Most Americans are familiar with pesticides and use them in their homes and yards on a regular basis. Sometimes more specifically referred to as insecticides or herbicides, products like ‘RoundUp’ and ‘Raid’ are staples of many sheds and garages. And why shouldn’t they be? It is difficult to deny their effectiveness or their utility.

But those two qualities which we appreciate pesticides for, have led to their overutilization and a tendency to gloss over some of their negative consequences. Just to provide a sense of scale, in 2012 alone the EPA reported that, even excluding the US agricultural industry which dwarfs all other sectors by far in their usage of pesticide, the American public consumer (those not representing businesses or commercial exterminators) spent $3.3 Billion on these products accounting for under a quarter of the total sales.

Why Cities are At Particular Risk

Urban areas like our very own San Diego, should take special care because they are particularly vulnerable to the consequences to the mass employment of pesticides. Cities have something referred to as urban runoff, which has a more pronounced effect than in urban areas rather than rural areas. This is because pesticides ordinarily are absorbed into the ground to varying degrees depending on sediment composition, how much clay or silt or sand is in the ground. (Bet you didn’t think dirt could be a little bit complicated right?) In rural areas, this is spread over a wide area,

keeping potentially dangerous buildup of chemicals from occurring. In cities where all the chemicals used to treat buildings can’t be absorbed into the ground they instead get pushed along by rain and deposit in concentrated areas, artificially creating those dangerous build ups we were just discussing.

As a point of illustration, we will return to our sunny city of San Diego and look at Tijuana rivershed, recognized by the National Oceanographic and Atmospheric Administration for being one of the last barriers between the pollutants our city produces and the Pacific Ocean. As a result of its bulwark role, it has collected significant concentrations of pollutants. One of which notably is a banned compound called chlordane. Chlordane has been prohibited for manufacture in the US since 1988 because of its ability to bioaccumulate and its toxicity.

Bioaccumulation is a term that describes how creatures at the bottom of the food chain possess some concentration of a chemical in their body. When they are eaten, the predator takes in all of the toxin that was in its food, for every meal it takes. This proceeds so on all the way up the chain and animals and humans alike can unwittingly expose themselves to dangerous toxins. In The Tijuana estuary samples were collected in 2018 by undergraduate students at the University of San Diego and determined to have concentrations as high as 227 parts per billion. Which sounds like a small number, only 227 out of a billion, but becomes a little more frightening when you consider the EPA limit in drinking water is 2 parts per billion.

WAIT, HOW IS THAT POSSIBLE IF IT’S BEEN BANNED 30 YEARS?

Without taking too much of a deep dive into organic chemistry, suffice it to say that chlordane belongs to a class of chemicals called organochlorides which are particularly difficult to break down naturally. The human body has a difficult time and nature has a difficult time trying to decompose it into something less poisonous to everything around it. Chlordane specifically has a half-life, the time it takes for half of the material to decompose when left to its own devices, of about 3500 days under the right conditions. Running some quick numbers, it takes five half-lives for a compound to be basically gone, so that would be 17500 days (or 47 years) for not quite all of the compound to disappear worst case scenario.

SO WHAT DO WE DO ABOUT IT?

The good news is cities and states can help speed the process along by treating soil and water and most already do. On an individual level, and this applies everywhere but remains especially true for cities, we can be more discriminating in our use of pesticides and do our best to not compound and prolong the problem. Not that I’m saying to let your home be overtaken by creepy crawlies, believe me I hate them just as much as the next guy, but maybe we can think a little bit more, and overreact a little bit less.

By Shearing Volkir

References:

Chlordane General Fact Sheet. Report. National Pesticide Information Center, Oregon State.

De Haan, David et al. USD environmental chemistry lab notebook

United States. EPA. Office of Pesticide Programs. Pesticides Industry Sales and Usage: 2008-2012 Market Estimates. By Donald Atwood and Claire Paisley-Jones.

Photo Credits: Pesticide images taken from non-copyrighted public domains. Products depicted are the property of their respective manufacturers, the writer of this post neither advocates for or against their use.

Runoff diagram courtesy of Essex Region Conservation Authority

Disclaimer: The opinions represented herein belong solely to the author and are not necessarily representative of the University of San Diego or the USD Department of Chemistry and Biochemistry.