Highly Conserved: Why Pesticides, Fungicides and Herbicides Are Bad For You

Yesterday I was in a bookstore and I succumbed to temptation. I brought home a copy of "Your Inner Fish: A journey into the 3.5 billion-year history of the human body," by Neil Shubin, because I just couldn't put it down. Shubin was one of the paleontologists who discovered the Tiktaalik, a fish with wrists and a neck that thrived in mudflats 380 million years ago, and is very probably one of our ancestral species.

This reminded me of all the things I loved about my biology classes, and why I briefly dreamed about being a paleontologist as a kid. But more germane to this blog, it reminded me why the toxins that get sprayed on crops are so very, very bad for us.

Highly Conserved

Conservation has a very specific meaning in genetics, somewhat different than its meaning in ecology. A conserved trait is one that has been preserved in multiple lines of descent from an original ancestor.

An example is the identical homeobox DNA sequences, making up what are called Hox genes, that we share with plants, insects, fungi and yeast, really anything with a body. Hox genes are variously responsible for embryonic development, bilateral symmetry (body development along an axis,) and body segmentation. Duplications of the homeobox gene segments in our line of ancestry have produced very complicated bodies using a chemical recipe that's readily recognizable in very divergent organisms.

Walk through our embryonic development, and our similarities to our earliest vertebrate ancestors are beautifully illuminated. At a little over three weeks, you can see the fish we came from.

As the book says, a scientific team "used work in flies to find a gene in chickens that tells us about human birth defects." Proteins that function in invertebrate anemones have a reliable function in forming back structures on vertebrate frogs. The same genes control eye production in mice and flies.

Our chemical similarities to other life forms run deep.

The Blueprints

There are DNA blueprints for building an entire animal, or plant, or fungi, in every living, non-reproductive cell of a diploid, adult being with a body. (Messy sentence? Guilty. But there are species whose haploid forms, gametes, which are equivalent in us to a sperm or egg, have independent lives. It's totally fascinating.)

How do similar or identical genes, made by the same set of DNA, produce such different critters? How does the body of a multicellular creature carrying many duplicates of identical DNA instructions produce such a divergence of tissues?

The answer to each question has some overlap: chemical signaling.

Genes produce instructions for a wide array of messaging chemicals to be sent out. In early development, these chemicals first begin to tell cells what they're supposed to be - the embryonic stem cells that could become anything start locking down unnecessary parts of their DNA so that only a limited set of instructions is available to it going forward. For anything with a body, the Hox genes send out the signals that make sure everything happens in the right order and goes where it's supposed to.

All throughout the life of the organism, chemical signals are sent out constantly to tell all these differentiated cells how best to work together. Considering that the genes controlling our earliest development have so many similarities, it shouldn't be too shocking that many of these signal chemicals have a lot in common, as well.

Hormones

The most well-known set of body-regulating chemical signals are hormones. They're produced by the endocrine system, a series of little glands and tissues that include the thyroid and adrenal glands, as well as the gonads, or main reproductive organs.

Our gonads produce the most famous of our hormones, estrogen and testosterone, but there are many others.

In those hormones, we come to one of the main reasons why the pesticides, fungicides and herbicides deployed to kill crop pests are so hurtful to us. If you click on the link in this sentence, it will take you to a comparison between some common animal and plant hormones with surprising similarities. (Click here for the full study.) You don't need to have studied chemistry yourself to see the duplicate structures in some of them.

Fungi are more closely related to us than plants. Insects are more closely related to us than fungi.

The surprise shouldn't be that things that hurt them hurt us, it should be that they aren't more hurtful to us, more often.

Disruption

A common means of harmful contamination in pesticides is endocrine disruption, sometimes through chemicals that mimic hormones. The defoliant Agent Orange contained dioxin as a byproduct of the manufacturing process, a molecule with a ring structure that fools the body's estrogen receptors and does enormous damage in the form of cancers and birth defects.

Dioxins are produced by many high temperature manufacturing processes, so they also end up in the coal fly ash and other industrial kiln ash that I wrote about the other day. This is one reason why it's probably a bad idea to grow food in these industrial byproducts, or put them out in the environment where they're likely to join any food chain.

Other crop pest toxins are directly disruptive of the endocrine system, whether by mimicking, neutralizing, or interrupting the production of, hormones. Yet others affect different body systems for the worse, in other ways.

And certainly, if these chemicals can hurt us, as they often can, they certainly aren't just harming one or two 'undesirable' species.

Rachel Carson originally sounded the alarm on this in Silent Spring, where she noted that DDT was hurting bird populations by making the shells of their eggs too thin to protect the chick from its mother's weight. DDT might be banned in the US, but it wasn't the only chemical known to cause problems. Other chemicals might cause problems, maybe worse ones, but we don't know because very little independently verified safety data is made available for them.

As Sandra Steingraber pointed out in Living Downstream, official government 'safe' levels for agricultural chemicals are often based on assuming that the levels likely to be found in food and the environment following common agricultural practices are perfectly fine. The official guidelines therefore get set by seeing what's normal and slapping a seal of approval on it.

We aren't all dead yet, how bad could it be?

Well, pretty bad. Some other time, though. The important thing to remember is that observable differences between species can be much larger than chemical differences between species. Go far enough back, we're related to those weeds we're trying to kill, which we should keep in mind as pesticide use expands along with genetically modified crop production.