This diary began as a comment on another, until it got so long and detailed I decided it was a diary in it's own right. The original diarist was upset because a careless pest control company had applied pesticides on the wrong property, and I chimed in to try and be of some assistance.
It made me realized that, as an environmental professional, I have some expertise on the subject of pesticides and other contamination that may be of use to the readers of this site. So, here is a not-so-brief primer on the history of pesticides and what can make them dangerous, which includes lots of links on where to go to get good data and information.
History of pesticides
There is a common misperception that 'bad' pesticides came into use in the period after World War II, when chemicals like DDT were introduced.
In fact, as bad as DDT was, it was a big improvement over previous pesticides. Before the post-war chemical era, many pesticides were metal-based--as in arsenic, lead, and copper. The sewers of Paris once ran with 'Paris Green', also known as copper arsenate, which was used to keep down the city's rat population. Around the turn of the century, Britain banned all apple imports from the U.S. because of the high level of lead and arsenic on American apples. Mercury was commonly added to outdoor paints to prevent mildew. And when an outbreak of a fever that was spread by ticks started killing off cows in the Southeast in the 10s and 20s, the U.S government ordered farms to dig big holes in the ground, fill it with an arsenic solution, and run all their cows through it.
It wasn't just in the U.S. In Italy in 1944 and 1945, they actually dropped arsenic from the sky in a desperate attempt to control the mosquito population, because of a malaria epidemic.
It is not that people did not understand how dangerous these substances could be to humans (although our understanding of chronic poisoning, as opposed to acute, is relatively new). During the Boer Wars, there were several generals who would go into farms, search the barn for cattle dip, and then pour it down the well.
So why would people use this stuff? Why would people use things that are so shockingly toxic?
The answer to why people were willing to drop arsenic out of airplanes is the same answer as to why we use toxic pesticides today: because taking care of pests is a pressing need. Rats, mosquitos and fleas have been one of mankind's one of the biggest nemeses. It can be easy to condemn the pesticide practices of farmers, when we are more removed from the harm that pests can cause. But it is a rare person, even the most organic of farmers, who will not use pesticides to control the fleas on her dog or keep termites from devouring his home. Pesticides are everywhere, from the DEET that keeps mosquitoes off of us to the mothballs that save our sweaters.
I am not defending all pesticides. We must be able to have clean drinking water and a clean environment. Whenever possible, people should implement Integrated Pest Management. I just want to set some context; when we look at the risks of pesticides, we must also weigh them against the considerable risks posed by pests. 'Pesticides are bad' is just not a reasonable position.
When is a pesticide dangerous?
The next question is to ask: how do we measure how dangerous a pesticide is?
Unfortunately, answering this question is not as easy as it seems on the surface. The Pesticide Action Network uses these criteriafor identifying 'bad actors':
* Known or probable carcinogens, as designated by the International Agency for Research on Cancer (IARC), U.S. EPA, U.S. National Toxicology Program, and the state of California's Proposition 65 list.
* Reproductive or developmental toxicants, as designated by the state of California's Proposition 65 list.
* Neurotoxic cholinesterase inhibitors, as designated by California Department of Pesticide Regulation, the Materials Safety Data Sheet for the particular chemical, or PAN staff evaluation of chemical structure (for organophosphorus compounds).
* Known groundwater contaminants, as designated by the state of California (for actively registered pesticides) or from historic groundwater monitoring records (for banned pesticides).
* Pesticides with high acute toxicity, as designated by the World Health Organization (WHO), the U.S. EPA, or the U.S. National Toxicology Program.
These are not terrible criteria (and I do not want to slam PAN, as they have high quality data on their site). But there is a significant problem. Except for the last criteria, these criteria do not address the most important aspect of toxicity: dose.
Toxicity is always in the dose. Grilling meat leads to the formation of the carcinogenic benzopyrene, but honestly, the dose is so tiny that your risk is minuscule. Water can be toxic at high enough doses. Just because something has toxic potential doesn't necessarily mean it's bad at low levels.
The most important piece of data to look at when evaluating the danger of a particular chemical is at what dose it may start to have a toxic effect, or at what dose it begins to pose a risk of cancer. The toxicity is quantifiable in a few ways.
These toxicity values are measured in reference concentrations (RfC), reference doses (RfD) for non-cancer effect, and slope factors for cancer risk. The RfC and RfD are estimates of the level of contamination that, if a person is exposed to that level of contamination on a daily basis, will not cause harm over a lifetime. RfCs are the safe concentrations in the air, and RfDs are safe oral doses.
Slope factors measure the cancer-causing potential of a compound. The slope factor is an estimate of the additional cancer risk, over a lifetime, caused by each incremental unit of exposure. It is called the slope factor because essentially, you plot your data on cases of cancer on a graph, and then draw a trend line through those plotted points. The steeper the line, the more carcinogenic the compound.
You can find these numbers for chemicals in the Integrated Risk Information System (IRIS).
When do you have an environmental threat on your hands?
The next big key, after toxicity, is the question of exposure. A chemical might be very poisonous. But just how likely are people to come in contact with it?
There are a lot of different chemical factors that affect the likelihood of exposure. A key one are solubility, or, if you want to get really science-y, the octanol-water partition coefficient. Both of these are ways to evaluate how likely is the chemical to migrate into water supplies. Some pesticides that are very bad, like the 'dirty dozen' pesticide Dieldrin, may be incredibly toxic. However, it poses less of a threat than it may otherwise because it will not get into the groundwater and spread rapidly. You have a problem if you have dieldrin at your site, but it's not going to be a problem that is going to effect all your neighbors. In general, as industry has worked to make chemicals that are less toxic to humans, they have also tried to make pesticides that are less soluble.
There a vast other number of chemical properties that can effect how dangerous a pesticide is. In general, a wealth of information about most common (and even some uncommon) pesticides can be found in the Hazardous Substances Databank.
Many of these chemical properties indicate how likely exposure may be, generally. But the danger posed by a particular compound can vary significantly site to site.
Just how bad a pesticide may be on a certain site depends on site-specific conditions (geochemistry, depth to groundwater, climate) and how they interact with certain chemical characteristics (adsorption to soil, solubility, and of course, toxicity) to create probably routes of exposure. Honestly, it can take a team of engineers working for a few months to figure out whether contamination actually poses a threat.
Well-intentioned environmental activists are often left in a difficult position--that of simply trusting that the investigators who have collected and analyzed all this data are on the up and up (since they don't have the resources to to do these analyses themselves). Most of the time, the investigators are on the up and up, but they aren't always.
So environmental groups do the best they can: sound the alarm about chemicals that CAN be dangerous, even though they usually can't really prove that a particular case of contamination is any more dangerous than the EPA and ATSDR have decided it is.
If you want more information about particular environmental contaminants (not limited to pesticides) and want to really get into the science of it, I recommend checking out the ATSDR's ToxFAQs. There are also more lengthy Toxicological Profiles, but those can be a bit hard to digest for a layman.
I am not trying to advocate any particular agenda. I know that many on this site are interested in environmental issues, and I thought you may be interested in some of the intricacies of pollution, especially pesticide contamination.
If this gets a good response, maybe I could do a whole series on the science of pollution, we'll see. Let me know if you would be interested!