62
River and Stream Sediments
absorption detector. The method determines simultaneously the following species in
a single sediment sample with a detection limit of 15/lg kg-I: tetraalkyllead (Me.Pb,
Me 3 EtPb, Me 2 Et 2 Pb, MeEt 3 Pb, Et.Pb), ionic alkyl lead (Me 2 Pb2+, Et 2 Pb 2 +, Me 3 Pb+,
Et 3 Pb+) and inorganic lead. Average recoveries oflead compounds from sediment by
this procedure were in the range 93-113 %. A sediment taken from the St Lawrence
River, Ontario was found to contain, (/lg kg- I as Pb) MeEt 3 Pb 142, Etlb 1152,
Et 3 Pb+ 187, Et 2 Pb2+ 22, Pb2+ 10,000, /lg kg- I with other lead species absent.
Reisinger et al. [160] used the gas chromatographic-atomic absorption spectrometric technique to demonstrate that biomethylation of inorganic lead does not account
for the presence of organolead compounds in sediments.
2.5.2
Mercury
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 oxidizing agents [161,
162].
Bretthaur et al. [163] described a method in which samples were ignited in a high
pressure oxygen-fIlled bomb. After ignition, the mercury was absorbed in a nitric acid
solution. Pillay et al. [164] 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 regia.
Feldman digested solid samples with potassium dichromate, nitric acid, perchloric
acid, and sulphuric acid [165]. Bishop et al. [166] used aqua regia and potassium
permanganate for digestion. Jacobs and Keeney oxidized sediment samples using
aqua regia, potassium permanganate, and potassium persulphate [167]. The approved US Environmental Protection Agency digestion procedure requires aqua regia
and potassium permanganate as oxidants [168].
These digestion procedures are slow and often hazardous because of the combination of strong oxidizing agents and high temperatures. In some of the methods,
mercuric sulphide is not adequately recovered. The oxidizing reagents, especially the
potassium permanganate, are commonly contaminated with mercury, which prevents
accurate results at low concentrations.
Earlier work on the determination of total mercury in river sediments also includes
that of Iskander et al. [169] and Craig and Morton [170]. Iskander et al. applied
flameless atomic absorption to a sulphuric acid-nitric acid digest of the sample
following reduction with potassium permanganate, potassium persulphate and stannous chloride. A detection limit of one part in 10 9 is claimed for this somewhat
laborious method. Craig and Morton [170] found a 2.2 /lg I-I mean total mercury level
in 136 samples of bottom deposits from the Mersey Estuary.
Early et al. [171] determined methyl-, ethyl-, and methoxyethylmercury compounds in sediments by leaching the sample with sodium iodide for 24 h and then ex-
River and Stream Sediments
absorption detector. The method determines simultaneously the following species in
a single sediment sample with a detection limit of 15/lg kg-I: tetraalkyllead (Me.Pb,
Me 3 EtPb, Me 2 Et 2 Pb, MeEt 3 Pb, Et.Pb), ionic alkyl lead (Me 2 Pb2+, Et 2 Pb 2 +, Me 3 Pb+,
Et 3 Pb+) and inorganic lead. Average recoveries oflead compounds from sediment by
this procedure were in the range 93-113 %. A sediment taken from the St Lawrence
River, Ontario was found to contain, (/lg kg- I as Pb) MeEt 3 Pb 142, Etlb 1152,
Et 3 Pb+ 187, Et 2 Pb2+ 22, Pb2+ 10,000, /lg kg- I with other lead species absent.
Reisinger et al. [160] used the gas chromatographic-atomic absorption spectrometric technique to demonstrate that biomethylation of inorganic lead does not account
for the presence of organolead compounds in sediments.
2.5.2
Mercury
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 oxidizing agents [161,
162].
Bretthaur et al. [163] described a method in which samples were ignited in a high
pressure oxygen-fIlled bomb. After ignition, the mercury was absorbed in a nitric acid
solution. Pillay et al. [164] 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 regia.
Feldman digested solid samples with potassium dichromate, nitric acid, perchloric
acid, and sulphuric acid [165]. Bishop et al. [166] used aqua regia and potassium
permanganate for digestion. Jacobs and Keeney oxidized sediment samples using
aqua regia, potassium permanganate, and potassium persulphate [167]. The approved US Environmental Protection Agency digestion procedure requires aqua regia
and potassium permanganate as oxidants [168].
These digestion procedures are slow and often hazardous because of the combination of strong oxidizing agents and high temperatures. In some of the methods,
mercuric sulphide is not adequately recovered. The oxidizing reagents, especially the
potassium permanganate, are commonly contaminated with mercury, which prevents
accurate results at low concentrations.
Earlier work on the determination of total mercury in river sediments also includes
that of Iskander et al. [169] and Craig and Morton [170]. Iskander et al. applied
flameless atomic absorption to a sulphuric acid-nitric acid digest of the sample
following reduction with potassium permanganate, potassium persulphate and stannous chloride. A detection limit of one part in 10 9 is claimed for this somewhat
laborious method. Craig and Morton [170] found a 2.2 /lg I-I mean total mercury level
in 136 samples of bottom deposits from the Mersey Estuary.
Early et al. [171] determined methyl-, ethyl-, and methoxyethylmercury compounds in sediments by leaching the sample with sodium iodide for 24 h and then ex-