Do Organophosphates cause ADHD?

Ever since Monday’s post I’ve been preoccupied thinking about that article which was mentioned in the comments section by Daniel . This article basically summarized a study that seemed to show that ADHD in children was related to exposure to organophosphate insecticides.

Articles like this appear all of the time in mainstream media and they scare the bejezus out of us because, after reading them, we end up thinking “Holy crap! We’re killing ourselves and ruining our society with these insane chemicals!” Most of the time, however, this just isn’t the case.  Look, if everything that the papers reported about the negative effects of pesticides and other chemicals was true we’d all have cancer, mental illness, or we’d just be dead.

After the above you’re probably telling yourself that I’m some kind of maniacal chemical apologist.  Maybe I am, but I don’t think so.  I’ve spent a lot of time reading the actual articles from which these media pieces are written and I like to think I have a relatively balanced view of these chemicals – maybe I’m deluding myself though – I’ve been known to do that on occasion.  In any regard, what I’m going to do with this blog post is to take a look at the media article and let you know some of the questions that I want answered before I get very concerned about the research, and by answered I mean answered by the scientific article from which the media piece was derived.  Now, to be fair, I have not read the actual scientific article from which this media piece was derived.  It isn’t online as I’m writing this (at least nowhere that I can find it), though I have no doubt that it will be soon.  I suppose that I could have waited to write this until it came out, in fact I considered that idea carefully, but instead I thought that I would tell you about the things that I’m wondering about the article; In other words, the things that I’ll be looking for when I finally get to read it.  Media people want POW!  Scientists want to know what’s actually going on.

Before we begin I should tell you that I’m no fan of organophosphates.  They include a wide range of chemicals (though they are, obviously, all related in that they’re organic chemicals with phosphorus), some worse than others – from the relatively tame orthene and malathion to the scary-as-hell disulfoton (aka disyston).  Right now, as an extension specialist who works with growers, I can tell you that organophosphate chemicals are, in general, not a preferred choice for most growers simply because there are so many safer and more effective choices out there.  My feelings about organophosphates can best be summed up by what I wrote in my book The Truth About Organic Gardening “[Organophosphates] are an old class of insecticides that has served its purpose and for the most part should probably go the way of the dodo, with the possible exception of orthene and one or two others.”

So here we go, the things that I will be looking for when I read the actual scientific article:

1.  What’s the confidence interval?  In the media article it was stated that children with higher levels of organophosphates were about two times more likely to have ADHD, but no confidence interval was given.  In epidemiological studies such as this the likelihood of a given outcome is usually expressed as an odds ratio.  In this case the odds ratio that a child would develop ADHD given a high level of organophosphate exposure would be about 2 (because it would be 2 times as likely that a child would develop ADHD as it would be if the child weren’t exposed to the organophosphates).  But in a scientific article the odds ratio will always be coupled with a confidence interval.  A confidence interval tells you how confident you are in your odds ratio.  If you’re very confident then you’ll have a narrow confidence interval – maybe 1.8-2.2 — which means that it is 95% certain that the odds ratio is between 1.8 and 2.2 (the 2.0 odds ratio is basically just the most likely point on the confidence interval for the odds ratio to sit.  It’s kind of like, but not exactly the same as, an average).  For an epidemiological study that’s darn good.  If that’s the confidence interval present in the article then I’ll be impressed.  What we might find though is a confidence interval of something like 0.2 to 22.  That stinks and you’re deluding yourself if you think that a confidence interval like this “proves” anything – unfortunately I have seen plenty of media articles use research with confidence intervals such as this because of the POW! factor.  They ignore the confidence interval and just look at the odds ratio.  My guess is that this article has something in between the two confidence intervals which I listed above – we’ll see.

2.  I want to know how often urine was sampled.
Organophosphates move through the body very quickly.  In fact, I was recently reading a paper which showed that you can’t predict from one test time to the next what organophosphate readings will be because there’s so little consistency.  If you’re exposed to an organophosphate one day you may test high that day, but two days later you’ll be testing low again, so, I want to know if a single sample was done – which I would consider to be almost useless in terms of telling us actual organophosphate exposure – or if multiple samples were taken over time which I would consider to be much more useful.

3.  Did the organophosphate really come from food?  The implication that these organophosphates which, in theory, contributed to the onset of ADHD came from food bugs me.  I want to see if the author actually draws this conclusion in the paper or if it was made up by the media.  There are lots of places that organophosphates are and have been used, the singling out of fruits, vegetables, or any food seems ridiculous to me.  The author of the media article points out that organophosphates are not used around homes much – but that really isn’t the case and it certainly wasn’t the case just a few short years ago. There are still plenty of organophosphates being used quite regularly around homes.  I just did a search for orthene and malathion and found that I could buy them quite easily online.  Diazinon and chlorpyrifos are two others that shouldn’t be used by homeowners but which I know of people using – sometimes in heavily trafficked areas.

4.  I’d like to know about how the other potential contributors to ADHD were controlled.  There are other things that have been correlated with ADHD, how were these controlled so we know they weren’t the cause of the ADHD measured in this experiment?  For example, abused or neglected children seem to have a higher rate of ADHD, how was this taken into account in the study?  Was it taken into account?  A theory would be (and I’m totally making this up) what if abused children are fed more food with higher rates of organophosphates while non-abused children are fed more organic food.  Then the results would show that the neglected kids had higher ADHD and higher organophosphates – but was it the poor parenting or the organophosphates which caused the ADHD?

So, those are the four questions that I’ll be asking right off – and there are more that I’ll think of once I actually read the article.  All of these questions don’t mean that I think the article is bad though – regardless of what their answers are.  This research was probably well conducted and will enlighten scientists and lead to new avenues of research.  But, I’m willing to bet that the POW! from the media article (ADHD is caused by eating organophosphates on food) isn’t quite as powerful when the whole article is read with a more critical eye.

Veggie garden safety

A few months ago I posted a caution about using old pressure-treated timbers for vegetable gardens (see my Sept. 23 posting).  I now routinely get questions about alternatives to these arsenic-laden materials, especially new treated lumber.  What’s in the new wood that makes it rot resistant, and is it dangerous?

Rather than arsenic, new pressure-treated lumber has copper as its active ingredient.  Though it also will leach out of the wood, there is not a human health hazard associated with its uptake by plants or animals.  You probably get more copper leaching into the water carried through your plumbing (assuming you have copper, and not lead, pipes).

What about plastic timbers?  Though I’ve not seen any literature about leachates from plastic lumber, I’ve seen some older plastic timbers that haven’t aged well – they can warp and twist.  I would avoid those made of rubber, because decomposing rubber produces leachates that are quite hazardous (see September 30 for a discussion on rubber mulches).

Of course, there are many other materials one could use to corral their veggies – concrete blocks, stone, natural wood, etc.  Do you have a favorite?  Post a comment to let us know!

Salt solutions

Hopefully everyone got their filling of turkey and dressing over the long Thanksgiving weekend.  I used our unusually mild weather on Saturday to celebrate a time-honored tradition around the Cregg farm: The annual cursing of the tangled Christmas lights.

Turning the calendar over to December in Michigan means another Midwest tradition is just around the corner as well: The annual dumping of the road salt.  Although totals vary, at least one source estimates that road crews pour 8 million tons of salt on roads in the US each year.  The effects of this sodium chloride are readily apparent on our vehicles – in Michigan it’s rare to see a vehicle more than 10 years old on the road – and drivers of those older cars that remain can usually see the road pass under them through a rusted-out floorboard.  Of course all this road salt has profound implications for landscape plants as well.  Sodium chloride can damage plants in several ways.  Both sodium and chloride can cause direct toxicity, particularly from salt-laden spray drift from highways.  Salt in soils can cause osmotic stress resulting in drought injury.  Sodium in soils can displace potassium, magnesium, and other essential plant elements.  High levels of chloride in plant tissue can reduce cold hardiness and make plants more susceptible to freezing injury.  Suffice to say that salt is bad for plants.

So what’s a plant lover to do?  In general I advise a two-phase strategy of Selection and Protection for homeowners and landscapers that have to deal with heavily salted roads.  By Selection I am referring to planting salt tolerant plants (or at least avoiding salt sensitive ones).  The poster child for a poor choice in Michigan is eastern white pine, which is extremely intolerant of road salt.  Witness this planting at a rest area along I-96 between Lansing and Detroit.

Don’t you love to see your tax dollars at work?  Even a cursory look at a list of salt sensitive plants would have been a tip-off that that white pines and highways are a bad mix.  Most blog readers should be able to come up with a list of salt tolerant or salt sensitive plants for their area by Googling their way around the internet.  A couple caveats about these lists:  First, many are based on anecdotal experience, not hard data, so you may see inconsistencies between lists.  If possible, try to consult several sources and look for a consensus opinion about the plants you’re interested in.  Second, many recommendations are dated and include plants that may be considered invasive or no longer recommended for planting.  One list I just looked at included Russian olive (invasive) and green ash (no longer planted in the Midwest due to Emerald ash borer).

Another approach to reducing salt damage to plants is Protection.  Here I am referring to erecting a physical barrier to block salt spray or salt splash from reaching plants.  The most typical form of barrier around here is a wooden frame or fence covered with burlap or canvas.  Some people will actually wrap their evergreen trees or shrubs with burlap.  This may help against winter desiccation but does little for salt since the salt-saturated burlap will still be in contact with the foliage.  Obviously aesthetics go out the window with the protection approach but I’m noticing more and more people are willing to put up with a couple of months of looking at burlap to keep their plants looking thrifty the rest of the year.  In northern Europe some road systems will line their roads with pre-formed plastic barriers to reduce salt splash to adjacent vegetation.

What about alternative deicers?  This is a question I get frequently when I speak about salt and plants.  There are several things to consider about alternative (i.e., not sodium chloride) deicers.  First is the cost. All alternative deicers are more expensive than salt, some by a factor of 10 times or more.  This often limits their widespread use for highway departments.  Many road crews will use alternative products around bridges and other sensitive areas where they want to limit corrosive damage.  Alternative products may also be useful for smaller scale operations such as parking lots and walkways.  Secondly, many alternative deicers contain calcium and/or magnesium chloride.  These may even be marketed as ‘plant safe’ since they contain calcium and magnesium, which are essential plant elements.  The problem is the chloride.  Chloride is a plant nutrient but is only needed in minute amounts (a few parts per million). At higher levels it becomes toxic.

A study in Colorado found tree damage due to chloride near roads which were treated with calcium and magnesium chloride for dust abatement.   For safer alternative deicers consider chloride-free products such as calcium magnesium acetate.

In the meantime here’s hoping for a mild winter for everyone.

My Least Favorite Pesticide

People often ask me about the most dangerous pesticides — the ones which they should be careful to avoid.  There are lots to choose from:  Di-syston (aka disulfoton) is really bad.  Rotenone has some potential problems that make it scary, as does copper sulfate.  But for my money the worst thing out there is something that isn’t even supposed to be used as a pesticide (at least not anymore) but which finds its way into our gardens thanks to recommendations from people like Jerry Baker:  Tobacco.

Despite its obviously “natural” origins, tobacco isn’t allowed by organic growers because of its drawbacks which I’ll mention below, but because it finds its way into so many “how-to” books it’s definitely worth knowing about this beast.

It’s easy to buy chewing tobacco, mix it with a little water, and apply it to whatever aphids or other insects that you see.  What’s even better is that tobacco really does work (just like Jerry says!).  In fact, for some things it works great.  For example, I’ve tried all kinds of barriers against slugs, and tobacco is the one that works the best, hands down — copper is kinda OK, diatomaceous earth takes a while but works fine — but man, tobacco really throws slugs for a loop.  Watching a slug try to go through a pile of tobacco is terrible (and yet morbidly entertaining!)  First, the slug approaches the tobacco at a snails pace (the snail is a close relative of the slug!)  Then the slug touches the tobacco….and then the fun begins!  The slug starts to move really fast — literally mouse walking pace — and then it stops — and then it shakes — and then it dies.  This all happens within four minutes.  The slugs in the picture below are all dead.

Despite my success I have a hard time recommending tobacco for slugs for two reasons.  The first is that it can carry plant diseases which can cause some major problems, and the second is that some dogs like to nibble at the tobacco — and they won’t let you know they’ve nibbled it until you let them back into the house (if you know what I mean)!

When a tobacco spray is used for insects the process is a bit different than just placing tobacco on the ground.  First, you mix tobacco with water, let it soak for awhile, filter the water out, and then spray it on the insects.  In the old days — the 1800s when this type of spray was popular — they would mix about a pound of tobacco with a gallon of water.  Jerry usually recommends much less.  The problem with recommending less than this is that at lower concentrations it doesn’t work nearly as well — but you really wouldn’t want to apply more because then the spray starts to get dangerous (because of higher nicotine concentrations).  So it’s a catch-22.  Don’t underestimate the toxicity of nicotine!  Also avoid underestimating the nastiness of the plant viruses that this stuff carries.

So what should you use instead?  A good insecticidal soap, or a spray with water are what I like to recommend.  If you must use something stronger then look for an insecticide with the active ingredient permethrin and follow the labeled instructions carefully (also make sure that the insect you want to control is on the label — if you can’t identify the insect you’re trying to control, or if that insect isn’t on the label, then don’t use a pesticide).  For slugs my favorite pesticide uses the active ingredient iron-phosphate.

Rubber mulch rubs me the wrong way

I’ve been receiving a lot of questions about rubber mulch lately.  For those of you not familiar with the product, it consists of shredded tires that can be dyed and used on ornamental landscapes or under playground equipment.  In fact, the Obamas had this material installed underneath their children’s play structure at the White House.  It seems an ideal way to recycle the 290 million scrap tires we generate annually.


But is it?

It’s not effective:  One of the main reasons we use mulch is to suppress weeds.  Research has demonstrated that organic mulches such as wood chips, straw, and fiber mats control weeds better than rubber mulch.

It burns:  You’ve heard stories about piles of scrap tires catching fire and burning for weeks.  Well, those same flammable compounds are in rubber mulch, too.  When compared to other mulch types, rubber mulch is the most difficult to extinguish once ignited.  In fact, some parks and playgrounds no longer use rubber mulch or rubberized surfaces because vandals have figured out that rubber fires cause a LOT of damage.

It breaks down:  Although sales literature would have you believe otherwise, rubber is broken down by microbes like any other organic product.  Specialized bacterial and fungal species can use rubber as their sole food source.  In the degradation process, chemicals in the tires can leach into the surrounding soil or water.

It’s toxic:  Research has shown that rubber leachate from car tires can kill entire aquatic communities of algae, zooplankton, snails, and fish.  While part of this toxicity may be from the heavy metals (like chromium and zinc) found in tires, it’s also from the chemicals used in making tires.  These include 2-mercaptobenzothiazole and polyaromatic hydrocarbons, both known to be hazardous to human and environmental health. 

It’s not fun to be around:  When rubber mulch gets hot, it stinks.  And it can burn your feet.  Yuck.

The EPA’s website says this about scrap tires:  “Illegal tire dumping pollutes ravines, woods, deserts, and empty lots.  For these reasons, most states have passed scrap tire regulations requiring proper management.”   So if we have legal tire dumping (in the form of rubber mulch), does that mean it doesn’t pollute anymore?

(You can read a longer discussion on rubber mulches here.)

Eat your veggies! (But not the arsenic, or the chromium, or the lead…)

vegetables_jpg.jpgThe last few years have been a perfect storm for the resurgence of home vegetable (and fruit) gardens.  Grapevines are trellised along sidewalks, herbs replace the grass in parking strips, and tiny gardens of carrots and lettuce are shoehorned into any available spot.  It’s all good  – but we need to be particularly careful about what those plant roots might be taking up along with nutrients and water.


1)  Contaminated soil.  Many urban (and suburban, and even rural) soils are contaminated with heavy metals, pesticides, and/or industrial wastes.  Lead is commonly found in soils near roads (from the old leaded gasoline we used to use) or from old lead-based paint chipping away from houses.   Arsenic is a very real problem in North Tacoma soils, for instance, thanks to the smelter that operated there for decades.   Overuse and incorrect use of home pesticides will leave residues in the soil for years.


2)  Contaminated compost and soil mixes.  Many of the same contaminants mentioned above can be found in unregulated composts and soil mixes.  (More on this topic here.)


3)  Treated lumber.  The old treated lumber (CCA = copper, chromium and arsenic) is no longer being sold, but it’s out there.  These timbers should not be used around vegetable gardens, as they will leach their heavy metals into the soil.  Vegetables vary in their ability to take up and store these metals.  (More on this topic here.)  Likewise, rubber mulches may leach unwanted chemicals into the soil and should not be used around food plants.  (More on this topic here.)

   garden_jpg.jpg    treated%20lumber_jpg.jpg

What can you do to avoid these problems?  A few things are quick, easy and cheap:

1)  Have your soils tested.  I’ve mentioned this in an earlier blog on urban soils.  It’s the best way to find out exactly what you have in your gardens – the good and the bad.

2)  Use only certified composts and soil mixes.

3)  Plant in containers if your soils aren’t safe for food.  This is especially easy to do with perennial herbs, which can be kept like any other container plant on your deck or porch for years.

4)  You can also replace the soil in your vegetable garden.  This isn’t quick, easy, or cheap, but is a solution for some people.