Here’s the information to help you decide
A couple of decades ago , lumber impregnated with chromated copper arsenate ( known as CCA ) was conceive the reply to a gardener ’s prayer . It vaunt long life than rot - repellent species likeredwood , you could buy it almost anywhere , and manufacturers said the treatment chemicals , though toxic , safely stay put in the wood . The main plus forgardenerswas that the chemicals did n’t harmplants , unlike creosote and pentachlorophenol , two previously pop wood preservatives .
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But then Word of God started seeping out that those CCA chemical substance were n’t so perfectly bound up after all , that some of them , in fact , migrated from the wood into the surroundingsoil . And that ’s when pressure - do by wood move into the raging seat .
What’s bad about pressure-treated wood?
In the imperativeness - treating process , timber is seal in a tank , and tune is evoke , create a vacuity . Then a solution hold atomic number 24 , atomic number 29 , and arsenic is add up . Because of the vacuum , the chemical are carry deep into the wood . Chromium is a bactericide , copper a fungicide , and arsenic an insect powder , and all stay decline of some form . All three are toxic , but chromium and copper do n’t heighten many concerns . If we do n’t breathe in it , chromium is not particularly harmful to us , and copper is n’t very toxic to mammals , although it is to aquatic life and fungi . It ’s arsenic that is worrisome .
Arsenic is everywhere . If this grey , metallic element - same element is flux with atomic number 8 , atomic number 17 , and sulphur , it ’s considered inorganic arsenic . If carbon is part of the compounding , then the white arsenic is constitutional . It ’s the inorganic forms that concern hoi polloi . The arsenate used in woodwind instrument handling is inorganic . compare to organic arsenic , inorganic arsenic is much more likely to accumulate in living tissues , where it interacts with cell enzymes and impairs metamorphosis . constituent soma of arsenic do n’t look to do this , and are largely excreted before they can do us impairment .
We ’re exposed to arsenic — mostly organic conformation — every day because very small amount are present in all soil , H2O , and food . We typically eat 25 to 50 micrograms ( a mcg is a one-millionth of a Hans C. J. Gram ) of mostly organic arsenic a day . downhearted levels of arsenic are in everything we eat . The biggest source is shellfish .
Inorganic arsenic also may be present in foods due to residues in the soil from the days when arsenic was an approve pesticide . One reason root craw tend to accumulate arsenic is that moment atom of soil stick to the theme ’s skin , even after a refreshing scouring . Peeling root vegetable before eating them gets rid of that arsenous oxide . Still , there ’s no need to worry about normal spirit level of arsenic in foods . The amount is so little it ’s not harmful .
Soils contain both organic and inorganic arsenic . Background levels of arsenic in grunge ( amounts due to geologic weathering , not to human contamination ) typically range from 0.1 to upwards of 10 parts per million ( ppm ) , and up to 40 ppm is look at tolerable , according to the U.S. Department of Agriculture . Above that level , noticeable amount come out showing up in minor ’s water , because Kyd ingest dirt .
urine contains backdrop arsenic too , but there might also be arsenic from contamination . The current EPA limitation for arsenic in boozing water is 50 parts per billion . In magnanimous doses , inorganic As is impregnable poison . Ingesting 1 to 3 milligram per kilogram of body weight can be disastrous . less amounts can cause nausea and diarrhea , scurvy production of both crimson and white blood cells , and give you a pins - and - needles sensation in your arms and legs . Inorganic ratsbane is also carcinogenic , increase the risk of lung , skin , and other cancers .
But as USDA heavy alloy expert Rufus Chaney points out , what constitutes an acute toxic dose is n’t really relevant to gardener . What we want to avoid are inveterate toxic doses , which can conduce to disease . Chronic exposure mean every day for a lifespan . According to the Agency for Toxic Substances and Diseases Registry ( ATSDR ) in Atlanta , we can have up to 0.3 micrograms of inorganic arsenic per kg of body weight per twenty-four hours and not be harmed . The average American fair sex , who weighs 132 lb . or 60 kilo . , would have to consume more than 18 micrograms daily all her life to see any ominous core . Before you get alarmed , remember this is inorganic arsenic we ’re spill about , not the constitutive character predominant in our dieting . And , an ATSDR voice point out , 0.3 mcg is a depleted appraisal for the maximal passable dot .
Testing for arsenic leaching and migration
I send soil samples from a 3 - class - honest-to-goodness CCA - framed bottom to a lab for testing . I take three samples at various space from the forest — right away side by side , several inches away , and in the middle of the bed . For a control , I place grease from a bed that ’s never been in contact with pressing - treated Sir Henry Joseph Wood . Only the soil very close to the treated Mrs. Henry Wood show a high - than - screen background level of arsenic .
The data on leaching
So how much arsenic leach into the soil from CCA lumber ? More to the point , how much gets taken up by vegetables ? And how much winds up in the mouth of child ? There have been a lot of field seem at the first two issues , but in judge to orchestrate the fact into meaningful information , I distinguish definitive answer can be problematical . I ca n’t tell you whether or not you should use pressure - treated Mrs. Henry Wood . What I can do is explicate the results of pertinent studies and give you the data you demand to decide for yourself .
CCA - treated wood does have upright ohmic resistance to leach , but there is some loss of chemicals . In a subject area of utility poles of varying ages , woodwind instrument scientist Paul Cooper of the University of New Brunswick in Canada found uniformly high CCA retention , clearly indicating that large amount of preservative had not leached out of the Mrs. Henry Wood . There seem to be an initial surge of leaching during the first rainy time of year , and then the wood resolve down to a ho-hum liberation of minor amounts , decreasing slightly over metre .
All three CCA element are more liable to leach at a pH of 3 or below , far too acidulent for growing vegetables . At levels of 4 and up , pH has no issue .
Cooper has also studied compost bins made of CCA Grant Wood , and witness that organic dot spring during the compost process cause more leaching . This not only bring more contaminants into the soil or compost , but also compromises the integrity of the lumber . Neither resultant role is suitable , so Cooper does not deliberate pressure - address wood suited for making compost BIN , although he does n’t object to using it in gardens . Finished compost has a near - neutral pH , so supply compost to CCA - frame beds is n’t a trouble .
Once arsenic is in the ground , it does n’t transmigrate much . Where there is leaching , arsenic grade drop apace with distance from the Sir Henry Joseph Wood , usually reach background levels within a few inches in leaven beds .
Some people have voiced fright that leached arsenic will encounter its way into groundwater , but Cooper ’s utility pole report found no grounds to sustain such concerns . Groundwater sample distribution taken from nigh to the poles had very miserable grade of CCA component . According to Stan Lebow , a Grant Wood scientist at the USDA ’s Forest Products Laboratory in Madison , Wisconsin , “ The potency for any CCA chemical substance drive into groundwater from garden habit is reasonably much zero . They just do n’t move that far . ”
If you use CCA lumber…
The chemicals in force per unit area - treat lumber are pesticide , so you should do by the wood with the same safeguard as befit any potentially hazardous material .
Protect yourself while work with CCA wood . Always wear gloves , middle protection , and most important , a dust masque . Long sleeves are a expert idea , too . Wash yourself and your clothes afterward . in conclusion , clean up every molecule of sawdust you could ( a shop vac does the best job ) . Drilling and sawing over a paved surface makes dust recovery wanton . Bag up sawdust and forest scrap and commit them to the landfill . Do n’t consider these steps optional .
Never , ever , burn CCA - treated wood . Burning station some of the arsenic up in smoke , which can be inhaled . The ash tree , too , contains gamy concentrations of arsenic .
There are things you’re able to do to CCA - treat wood to minimize leach or migration . Scrubbing the Mrs. Henry Wood with detergent or power wash it will take away surface residuum . If possible , let the board brave for several calendar month after they ’ve been cut and drilled before assembling . study show the big amount of leach occurs the first showery time of year . Always predrill holes for screws , which will preclude crack in the woodwind instrument . Cracks are places where preservative can percolate . line the inside of the bottom with heavy - tariff charge card before filling it will make a strong-arm barrier to any CCA compounds moving into your soil . house painting discover wood surfaces with water - repellant goal , key , or stain will protect your pelt if you lean or kneel on the side . And if you have little fry , it will also forbid CCA compound moving from little hands to piffling mouth .
ultimately , you’re able to take reward of arsenic ’s leaning to not trip far in the filth . To keep the arsenic in place , desist from blend grease along the perimeter few inches of the bed with grunge far in . Avoid growing prickly-seeded spinach and root crop , particularly carrots and radishes , tight to CCA - treated wood . Consider plant a band of thick flowers along the edge of the layer .
The story on arsenic and vegetables
There have been three major studies of vegetables get in arsenic - enhanced soils , one by E.A. Woolson ( United States , 1973 ) , one by C. Grant and A.J. Dobbs ( Britain , 1977 ) , and one headed by T.W. Speir ( New Zealand , 1992 ) . All measured arsenic ’s consequence on plant growth and arsenic content of the harvest .
At sure levels of concentration , arsenic interferes with plant growth , but it ’s unimaginable to popularise about amounts . Availability to flora vary from soil to soil , and sensitivity diverge from crop to crop . Beans are fairly sensible , while carrots and tomatoes tolerate arsenic well . Very small addition of arsenic can really increase yields . Also , there ’s no correlation coefficient between a craw ’s sensitivity to arsenic and the ability to take up and translocate it to edible plant life parts .
Available arsenic — meaning arsenic in a form works can absorb — is a much more important step than total arsenic . Typically , background arsenic is either pretty much insoluble or is tie up in a complex relationship with mineral and constitutive subject . For good example , in the Grant and Dobbs study , soil with 24 ppm total arsenic had 7 ppm available As . At 14 ppm total arsenic , available arsenous oxide was insensible .
Arsenic accumulates in very small amounts in vegetables , but generally in percentage we do n’t corrode . Grant and Dobbs grew greenish noggin , carrot , and tomatoes for their tryout . Crops grown in territory with 24 ppm total arsenic had the following arsenic levels in the edible parts : dark-green bean , 0.29 ppm ; carrot , 0.11 ppm ; and tomato , 0.14 ppm . These , too , are total arsenic levels , and as Rufus Chaney pointed out , much of it would be organic . Carrots , for model , produce in stain with no add arsenic contained 0.05 ppm arsenic .
Woolson tested green and lima beans , spinach , cabbage , tomatoes , and radish . Radishes and spinach took up the most arsenic , but even in territory with enough ratsbane to decoct outgrowth by 50 % , the spinach had only about 1 ppm arsenic and the radishes about 8 ppm . After the experiment , Woolson feel available arsenic in the stain had been reduced in “ barely important ” amounts , designate the plants had removed very , very modest dower .
In general , plants lean to hold what arsenic they accumulate in their antecedent , typically in the fibrous roots . Uptake into plant tops and fruits is very small . ( As always , there are exceptions . Carrots , radishes , and spinach all tend to stack away arsenic in their eatable portions . )
For exercise , beets are good arsenic accumulator , but most stay in the tail - like root , not the bulbous part you eat . In Speir ’s experimentation , common beet raise on soil with 66 ppm arsenic contained less than 10 ppm arsenic after being completely dry out . To put this in perspective , at overbold weight unit — the agency vegetables are actually eat — that concentration would be only about 2.5 ppm . And if you remove the skin , you also remove much of that arsenous anhydride . An interesting footnote : In the Speir study , crop were grow in filth incorporate CCA - treated sawdust . Because sawdust has a Brobdingnagian proportion of surface arena , it leaches chemicals at a very high pace , so in upshot this is a bad - case experiment .
So is CCA-treated wood unsafe?
I went to several scientists to get their take on the data in the various report .
Les Bourquin , a food rubber specializer at Michigan State University , says , “ Consumers as a whole would like to have zero risk . The classic example is , you ’re safer in an plane than you are in a railroad car . But most people are more comfortable drive a elevator car because that ’s where they ’re in ascendance . There are some things we do in our life sentence that put us at much greater risk ” than eating food spring up in CCA - framed beds . Bourquin feels that from a nutrient safety standpoint , microbial contamination like E. coli 0157 : H7 is of much greater concern . “ Compared to microbial risks , arsenic picture does n’t seem a bounteous problem . ”
Rufus Chaney at the USDA concur with Bourquin about nutrient safety . “ There ’s no grounds that food for thought rubber is impaired by produce vegetables around CCA - plow wood . ” According to Chaney , high levels of inorganic white arsenic in soil will kill a plant before there ’s enough ratsbane in the plant itself for you to consider not eating it . Far more important is the risk of infection of potential transfer of arsenic to skin and backtalk , particularly for children , whose minor bodies do n’t abide arsenic as well as ours do . Chaney points out that unrelenting leaching , however minuscule , means that arsenic is continually coming to the surface of the wood , where it can easily be transferred to us or our children when we touch the woodwind . “ There ’s just no path around it , ” Chaney suppose . “ For me , this is the overrule reason not to utilize CCA . ”
ACQ, a New Alternative
Public business concern over potential hazards of CCA has lead the diligence to look for safe , less controversial preservatives . A few years ago , one of the producer of CCA came out with a preservative touted as environmentally sound . ACQ ® , which stand for alkaline copper quat , is a mixture of fuzz and a quaternary ammonium compound , nicknamed quat . Small amounts of copper and quat do percolate , but nothing in ACQ is considered hazardous by the EPA , and no factor is a known or suspected carcinogen . The maker , Chemical Specialties , Inc. ( CSI ) , use only recycle pig in ACQ . The wood is have a bun in the oven to last as long as CCA - cover lumber .
I first heard about ACQ four years ago , but had never found a place to bribe it . Why , I wondered , was it so unavailable if it had so much to advocate it ? The first version to go on the grocery store check no water repellent and had to be treated by the buyer to denigrate cracks and warp . In previous 1997 , CSI came out with a edition , ACQ Type D , which has a build - in water repellant . The company hop the new conceptualisation will be more attractive to pound retailer and consumers . ACQ - treated wood is about 10 % more expensive than CCA because it contains more fuzz .
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