Arsenic

[Iggle piggle]

Hi, I'm new here and I was wondering if anyone knows how dangerous arsenic is in a domestic garden environment? Would levels of 160 ppm in the soil make growing vegetables dangerous? Does anyone know how much of that arsenic is likely to move in the soil and water if the soil is disturbed? If the soil was moved a lot during construction could the arsenic move in any dust produced and how dangerous would that be to human health? I have no scientific background other than basic soil science in horticulture and I am finding it hard to get much information on contaminated ground. Thanks

[YT2095]

the problem here is that different plants take up different elements in different amounts and so it`s impossible to determine.

also it`s very unlikely unless the site is freshly contaminated that there will be any elemental arsenic present, it`s likely to be locked-up as arsenides and arsenates (these are the most stable),

it`s worth a mention that arsenic although Toxic esp as gaseous (hydrogen arsenide/ arsine) is not a Cumulative poison like some heavy metals for example, and is cleared from the system with relative ease in small doses.

 

in a nutshell, without more specific data and a site survey it`ll be impossible for anyone to give you an exact reply.

[insane_alien]

according to http://www.bgs.ac.uk/britainbeneath/land_arsenic.html

 

the guideline value is 20 mg /kg of 20 parts per million.

 

growing stuff is fine but i wouldn't recommend eating them. i don't think dust would be too much of an issue. if its dusty just dampen the ground with a hose.

[hermanntrude]

grow stuff which absorbs arsenic for a few years but throw it all away. Then re-test the soil... it should be an efficient way of cleaning the soil.

[insane_alien]

and remember to dig up the soil every time you start growing a new batch so you mop up the arsenic into some of the deeper soil. this will make it less likely that future crops will contain elevated levels of arsenic.

 

the quicker route, would be to skim the topsoil off and buy new topsoil. but that is likely to be expensive.

[YT2095]

"Plant uptake of arsenic in vegetables grown in garden soils contaminated with arsenic from mining activity in south-west England has also been reported (Thornton, 1994). In this study, 32 home garden sites were examined. The soil arsenic at these sites ranged from 144-892 mg/kg and averaged 322. In normal agricultural soils in England the range is 2-53 mg/kg As with an average of 10 mg/kg As. The arsenic content was determined in six garden crops: lettuce, onion, beetroot, carrot, pea and bean. The arsenic uptake (mg/kg dry weight) was species dependant with the highest amount in lettuce (average 0.85, range 0.15-3.9, n=28) and lowest in beans (average 0.04, range 0.02-0.09, n=7). The effects of soil constituents such as iron, phosphorus, and calcium on arsenic uptake were examined. In lettuce, the uptake increased with increasing phosphorus in the soil and decreased with increasing iron content, presumably due to competitive sorption reactions between phosphorus and arsenic in the soil and with precipitation reactions with the iron to form insoluble iron arsenates. The UK statutory limit of 1 mg/kg As (fresh weight) was not exceeded in any of the vegetable samples."

 

taken from: http://www.noccawood.ca/stilwell1.htm

 

So... it would seem that Iron is your Friend, which is good because a bag of iron sulphate is readily available at almost all gardening stores and is really inexpensive (it`s usually sold as Moss killer).

[John Cuthber]

It seems unlikely that plants would take up enough arsenic from the soil to be toxic. However it would make sense to have the first crop of any plant tested.

[Iggle piggle]

Thank you everyone for your replies. The mean arsenic level is approx. 160ppm but some areas are 1200ppm and the plan is to re soil to 600mm and line with a permeable membrane, would this stop the arsenic moving and re contaminating the fresh soil ? The area is approx 7 acres with pH varying from 4.2 to 9.1. This is in Cornwall UK with an old tin mine within 150m but it is not clear if the contamination is from mine spoil or underlying rock. Borehole samples to 1m show random contamination from the top to the bottom of the samples with no clear pattern. At the higher levels does this pose a problem to health if you are in contact with the soil ?