Environmental Engineering Reference
In-Depth Information
Soil was taken from sample C, with high concentrations of As and 100 g was added
to each of the three beakers. Deionised and filtrated (Milli-Q) water was thereafter
added to each beaker (L/S = 6). The first beaker was left undisturbed in an air/
oxygen environment; the second was left undisturbed under anaerobic conditions
by means of nitrogen gas gently bubbled into the water phase. In the third beaker,
soil and water was vigorously stirred in an air/oxygen environment. After 20 h,
water samples were taken from all beakers. The samples were filtrated through 0.45
mm cellulose acetate filters and the filtrates were sent for analysis of total As,
As(III), As(V), DMA and MMA concentrations. The stirred sample was difficult to
filtrate because the filter became clogged by particles and therefore this sample was
pre-filtrated through a 1.2 mm micro fiberglass filter.
Leaching tests were carried out following a standardized procedure with two-
step leaching (SS-EN 12457-3). In the first step, the soil was shaken with Milli-Q
water (L/S = 2) for 6 h. The leachate water was filtrated and sent to the laboratory
for chemical analysis. The sample was thereafter shaken again (L/S = 6) for 18 h
and the leachate filtrated and sent for chemical analysis of total As.
Groundwater samples were collected on three occasions from the same well in
the contaminated area around the former impregnation barrel. Before sampling,
the groundwater well was turned over five times. On the first sampling occasion the
groundwater was not filtrated in the field. On the second and third occasion the
water was filtrated in the field and samples taken with a pump with an attached
filter (0.45 mm) in the groundwater tube. All samples were collected in plastic
flasks filled up to the top, sealed with a lid and stored cold.
The soil samples, that is the original 52, the new mixed samples A-C, and
the groundwater samples were analyzed for concentrations of total As, other
elements and dry substance by a certified environmental laboratory. For each
sample, 1 g of dried soil was microwave digested in nitric acid and hydrogen
peroxide. The samples were subsequently filtered or centrifuged (depending on
particle content) before analysis. Total element concentrations were analyzed by
inductively coupled plasma atomic emission spectroscopy (ICP-AES). Loss of
ignition was determined at the Chemical Environmental Laboratory at Chalmers
following a standardized procedure.
The mixed soil samples A-C, leachates from the laboratory experiments and
the groundwater samples were analyzed for concentrations of the following
As species: arsenite/As(III), arsenate/As(V), monomethylarsonic acid (MMA) and
dimethylarsinic acid (DMA) by a certified environmental laboratory. The laboratory
is not certified for the As speciation method, but the analyses were carried out
by specialists in a research group at a Swedish university. One gram of the soil
sample was treated with a phosphate buffer to leach the arsenic. The leachate
was then centrifuged and filtered through a 0.45 mm filter. Immediately prior to
analysis, the sample was acidified to 0.07 M with HNO3 and diluted. Samples
were analyzed by ion chromatography inductively coupled plasma mass spec-
trometry (IC-ICP-MS). Leachates and groundwater samples were only filtered
through a 0.45 mm filter and subsequently treated and analyzed in the same way
as the soil samples.
