Burnt alun shale and lime is the residual product that was formed when alun shale was
used as fuel to convert limestone to quick lime. The material contains arsenic, vanadium,
molybdenum, cadmium, nickel, lead, and uranium among other elements. The aim of this
paper is to examine the uptake of trace elements in vegetables grown on burnt alun shale
and lime to determine whether or not the surrounding environment and humans are
exposed to these elements by eating plant products.
A cultivation trial was carried out where onion, carrot, and lettuce were grown on three
mounds of burnt alun shale and lime in the Falköping area in Sweden. The treatments
were burnt alun shale and lime mixed with peat, only burnt alun shale and lime, and a
reference soil. The reference plots were natural soil mixed with peat adjacent to the
mounds. After harvest the vegetables were dried and weighed in order to determine the
growth. Growth medium samples were analyzed for the plant available fraction of
arsenic, vanadium, molybdenum, cadmium, nickel, and lead. Plant samples were
analyzed for the total content of the above-mentioned trace elements. Particle size
distribution, organic matter content and pH was also determined for the growth medium
samples.
The growth of the vegetables was, as expected, higher with the treatment with burnt alun
shale and lime mixed with peat compared to the treatment with only burnt alun shale and
lime. The treatment with only burnt alun shale and lime gives higher concentrations of
trace elements in the vegetables, than the treatment with burnt alun shale and lime mixed
with peat. There is a positive correlation between the concentration of NH4NO3-
extractable arsenic, vanadium, molybdenum, and cadmium in the growth medium and the
concentration in the vegetables. The correlation between the concentration of NH4NO3-
extractable nickel and lead in the growth medium and the concentration in the vegetables
is on the other hand slightly negative. Lettuce is the vegetable that generally contained
the highest concentrations of trace elements compared to onion and carrot.
No conclusions could be drawn on whether the pH had any effect on the contents of trace
elements in the growth medium or the uptake in the vegetables. Nor has the particle size
distribution or the organic matter content had any visible effect on the content of trace
elements in the growth medium or in the vegetables.
The quantity of molybdenum in carrot on one square meter cultivation area at the trial site Rörsberga exceeds the limit value for human daily intake. This is the only exceeded value for carrot and for onion no value on quantity exceeded the limit values. For lettuce on one square meter cultivation area at Rörsberga, the limit value is exceeded for the quantity of arsenic, vanadium, molybdenum, and cadmium. At the trial sit...
