14
River and Stream Sediments
2.7.9
Mercury
Cold vapour atomic absorption and plasma emission spectrometric techniques [16]
have been used extensively for the determination of mercury in river sediments
[13-15,17]. Sediment digestions have been carried out using nitric-sulphuric acid
then potassium permanganate-potassium persulphate [13,14,17] and potassium persulphate oxidation-stannous chloride reduction [15]. Jirka and Carter [15] claim a
relative standard deviation of 6 % at the 20-30 mg kg-I level for an automated cold
vapour atomic absorption method whilst Agemian and Chau [17] claim 14 % at the
0.1 mg kg-I level and 2 % at the 2 mg kg-I level.
2.7.70
Silver
The polarized Zeeman flame atomic absorption method described under cadmium
[7] has also been applied to the determination of silver in river sediments. The
detection limit was 0.1 mg kg-I based on a 0.2 g sample size and a 25 ml final solution
volume. Silver was evaluated using the 328.1 nm line and air-acetylene flame. A
certified reference sediment which had been shown by isotope dilution mass spectrometry to contain 6.41lg I-I silver in the digest was shown by this method to contain
5.6 Ilg I-I silver, i. e. 88 % recovery.
Table 2.8
Sequential chemical extraction procedure carried out on 1 g dry weight of lake sediment
(from [7])
Extractant
(a) Sediment depth;
0.75 moll-I LiCI - 0.25 moll-I CsCI
-60 % MeOH (10 min @ 20°C)
1 moll-I CH 3 COONa, pH 5.0
(5 h @ 20°C)
1 moll-I NH 2 0H.HCl - 25 %
(2 h @ 20°C)
H 2 0 2 , pH 2
(5h @ 90°C)
Aqua Regia - HF - HCl- Hz02
(b) Sediment depth;
0.75 moll-I LiCI - 0.25 moll-I CsCI
-60 % MeOH (10 min @ 20°C)
1 moll-I CH 3 COONa, pH 5.0
(5 h @ 20°C)
1 moll-I NH 2 0H·HCl - 25 %
CH 3 COOH
(2 h @ 20°C)
Hz0 2 , pH 2
(5h @ 90°C)
Aqua Regia - HF - HCl - H 2 0 2
In extract
0- 1 em;
% of total silver
(total silver content
5.53mgkg- l )
Readily extractable
9.4
Carbonate bound surface
0.5
- oxide bound ions
Ions bound to Fe-Mn oxides
0.5
Organically and sulphide bound ions 41.8
Ions bound to the residual phase
32 - 33 cm;
Readily extractable ions
Carbonate bound surface
- oxide bound ions
49
(total silver content
1.00mgkg- l )
3
Ions bound to Fe-Mn oxides
3
Organically and sulphide bound ions 16
Ions bound to the residual phase
84
River and Stream Sediments
2.7.9
Mercury
Cold vapour atomic absorption and plasma emission spectrometric techniques [16]
have been used extensively for the determination of mercury in river sediments
[13-15,17]. Sediment digestions have been carried out using nitric-sulphuric acid
then potassium permanganate-potassium persulphate [13,14,17] and potassium persulphate oxidation-stannous chloride reduction [15]. Jirka and Carter [15] claim a
relative standard deviation of 6 % at the 20-30 mg kg-I level for an automated cold
vapour atomic absorption method whilst Agemian and Chau [17] claim 14 % at the
0.1 mg kg-I level and 2 % at the 2 mg kg-I level.
2.7.70
Silver
The polarized Zeeman flame atomic absorption method described under cadmium
[7] has also been applied to the determination of silver in river sediments. The
detection limit was 0.1 mg kg-I based on a 0.2 g sample size and a 25 ml final solution
volume. Silver was evaluated using the 328.1 nm line and air-acetylene flame. A
certified reference sediment which had been shown by isotope dilution mass spectrometry to contain 6.41lg I-I silver in the digest was shown by this method to contain
5.6 Ilg I-I silver, i. e. 88 % recovery.
Table 2.8
Sequential chemical extraction procedure carried out on 1 g dry weight of lake sediment
(from [7])
Extractant
(a) Sediment depth;
0.75 moll-I LiCI - 0.25 moll-I CsCI
-60 % MeOH (10 min @ 20°C)
1 moll-I CH 3 COONa, pH 5.0
(5 h @ 20°C)
1 moll-I NH 2 0H.HCl - 25 %
(2 h @ 20°C)
H 2 0 2 , pH 2
(5h @ 90°C)
Aqua Regia - HF - HCl- Hz02
(b) Sediment depth;
0.75 moll-I LiCI - 0.25 moll-I CsCI
-60 % MeOH (10 min @ 20°C)
1 moll-I CH 3 COONa, pH 5.0
(5 h @ 20°C)
1 moll-I NH 2 0H·HCl - 25 %
CH 3 COOH
(2 h @ 20°C)
Hz0 2 , pH 2
(5h @ 90°C)
Aqua Regia - HF - HCl - H 2 0 2
In extract
0- 1 em;
% of total silver
(total silver content
5.53mgkg- l )
Readily extractable
9.4
Carbonate bound surface
0.5
- oxide bound ions
Ions bound to Fe-Mn oxides
0.5
Organically and sulphide bound ions 41.8
Ions bound to the residual phase
32 - 33 cm;
Readily extractable ions
Carbonate bound surface
- oxide bound ions
49
(total silver content
1.00mgkg- l )
3
Ions bound to Fe-Mn oxides
3
Organically and sulphide bound ions 16
Ions bound to the residual phase
84