184 Organic compounds in soils, sediments & sludges
This automated procedure was estimated to have a precision of 0.13–
0.21 mg Hg kg
−1 at the 1 mg Hg kg
−1 level with standard deviations varying from
0.011 to 0.02 mg Hg kg
−1 , i.e. relative standard deviations of 8.4–12% at the 17.2–
32.3 mg Hg kg
−1 level in sediments. Recoveries in methyl mercuric chloride spiking
studies were between 85 and 125%.
Robert and Robenstein et al [81] carried out indirect determination of Hg
119 by
preparing NMR spectra of methylmercury complexes, e.g. CH 3 Hg
2+ thiol ligands in
sediment samples.
Feldman digested solid samples with potassium dichromate, nitric acid, perchloric
acid and sulphuric acid [62]. Bishop et al [63] used aqua regia and potassium permanganate for digestion of organomercury compounds. Jacobs and Keeney oxidised
sediment samples using aqua regia, potassium permanganate and potassium persulphate [64]. The approved US Environmental Protection Agency digestion procedure
requires aqua regia and potassium permanganate as oxidants [82].
These digestion procedures are slow and often hazardous because of the combination of strong oxidising agents and high temperatures. In some of the methods,
mercuric sulphide is not adequately recovered. The oxidising reagents, especially the
potassium permanganate, are commonly contaminated with mercury, which prevents
accurate results at low concentrations.
In lakes and streams, mercury can collect in the bottom sediments, where it may
remain for long periods of time. It is difficult to release the mercury from these matrices for analysis. Several investigators have liberated mercury from soil and sediment
samples by the application of heat to the samples and the collection of the released
mercury on gold surfaces. The mercury was then released from the gold by application
of heat or by absorption in a solution containing oxidising agents [84, 85].
Batti et al [83] determined methylmercury in river sediments from industrial and
mining areas.
Bretthauer et al [66] described a method in which samples were ignited in a highpressure oxygen-filled bomb. After ignition, the mercury was absorbed in a nitric acid
solution. Pillay et al [67] used a wet-ashing procedure with sulphuric acid and perchloric acid to digest samples. The released mercury was precipitated as the sulphide.
The precipitate was then redigested using aqua using aqua regia.
As the concentration of organomercury compounds encountered in actual sediment samples can occur at levels as low as 0.00001–0.004 mg kg
−1 (Table 7.3).
Considerable experimental skill is needed to adapt methods such as preconcentration
that will give results on actual samples that have a very low level of contamination.
7.5 ORGANOSILICON COMPOUNDS
Pellenberg et al [87] analysed river sediment for silicone content by nitrous oxideacetylene flame atomic absorption spectrophotometry. He showed that total carbon
and total carbohydrates both correlate with silicone content and the correlation
between sedimentary silicone and presumed sewage material is good enough to
suggest silicone as a totally synthetic, specific tracer for sewage in the aquatic
environment.
This automated procedure was estimated to have a precision of 0.13–
0.21 mg Hg kg
−1 at the 1 mg Hg kg
−1 level with standard deviations varying from
0.011 to 0.02 mg Hg kg
−1 , i.e. relative standard deviations of 8.4–12% at the 17.2–
32.3 mg Hg kg
−1 level in sediments. Recoveries in methyl mercuric chloride spiking
studies were between 85 and 125%.
Robert and Robenstein et al [81] carried out indirect determination of Hg
119 by
preparing NMR spectra of methylmercury complexes, e.g. CH 3 Hg
2+ thiol ligands in
sediment samples.
Feldman digested solid samples with potassium dichromate, nitric acid, perchloric
acid and sulphuric acid [62]. Bishop et al [63] used aqua regia and potassium permanganate for digestion of organomercury compounds. Jacobs and Keeney oxidised
sediment samples using aqua regia, potassium permanganate and potassium persulphate [64]. The approved US Environmental Protection Agency digestion procedure
requires aqua regia and potassium permanganate as oxidants [82].
These digestion procedures are slow and often hazardous because of the combination of strong oxidising agents and high temperatures. In some of the methods,
mercuric sulphide is not adequately recovered. The oxidising reagents, especially the
potassium permanganate, are commonly contaminated with mercury, which prevents
accurate results at low concentrations.
In lakes and streams, mercury can collect in the bottom sediments, where it may
remain for long periods of time. It is difficult to release the mercury from these matrices for analysis. Several investigators have liberated mercury from soil and sediment
samples by the application of heat to the samples and the collection of the released
mercury on gold surfaces. The mercury was then released from the gold by application
of heat or by absorption in a solution containing oxidising agents [84, 85].
Batti et al [83] determined methylmercury in river sediments from industrial and
mining areas.
Bretthauer et al [66] described a method in which samples were ignited in a highpressure oxygen-filled bomb. After ignition, the mercury was absorbed in a nitric acid
solution. Pillay et al [67] used a wet-ashing procedure with sulphuric acid and perchloric acid to digest samples. The released mercury was precipitated as the sulphide.
The precipitate was then redigested using aqua using aqua regia.
As the concentration of organomercury compounds encountered in actual sediment samples can occur at levels as low as 0.00001–0.004 mg kg
−1 (Table 7.3).
Considerable experimental skill is needed to adapt methods such as preconcentration
that will give results on actual samples that have a very low level of contamination.
7.5 ORGANOSILICON COMPOUNDS
Pellenberg et al [87] analysed river sediment for silicone content by nitrous oxideacetylene flame atomic absorption spectrophotometry. He showed that total carbon
and total carbohydrates both correlate with silicone content and the correlation
between sedimentary silicone and presumed sewage material is good enough to
suggest silicone as a totally synthetic, specific tracer for sewage in the aquatic
environment.