24
River and Stream Sediments
(d) As in (b) but digested in 100 ml of 1 N hydroxylamine hydrochloride plus 25 %
acetic acid solution.
(e) As in (b) but digested in 100 ml of 0.05 N EDTA solution of pH 4.8.
Fig. 2.2 a-g presents the levels of cadmium, copper, lead, zinc, nickel, chromium and
cobalt along the river, using the four partial extraction methods, together with a total
extraction method involving Parr bomb digestion. For cadmium, the total and 4.0 N
nitric acid plus 0.7 N hydrochloric acid levels were not obtained because the small
sample size used in these methods did not provide enough metal in solution to give a
detectable signal. The anomalous regions are visually quite apparent in spite of the
small number of samples used, cadmium, copper, lead, zinc, and nickel showing very
well defmed anomalies with all methods. For chromium this is less clear, while no
significant anomalies are seen for cobalt. Fig. 2.3 a-c provide similar data for iron,
manganese and aluminium. These three are major elements and they have no significant anomalies. All methods, except the total and 4.0 N Nitric acid plus 0.7 N hydrochloric acid, provide the same type of anomalies and the same distribution of metal levels
along the river. This means that the three weaker extraction methods (0.5 N hydrochloric acid, 1 N NHpH·HCI plus 25 % acetic acid and 0.5 N EDTA) attacked essentially the
same part of the sediment. The other two methods showed the same type of distribution
as the three weaker methods only in the cases of copper, lead, zinc, nickel and manganese. The absolute amount of metal extracted decreases as the extracting solution becomes weaker. Of the partial extraction methods, the 4.0 N nitric-hydrochloric acid
solution is highest followed by the 0.5 N hydrochloric acid solution. The amount of
metal extracted by the other two weaker solutions, relative to each other, depends on
the metal involved. Table 2.14 shows the mean background levels of each metal in the
Rideau River sediments calculated by excluding the anomalous samples.
The extracting efficiency of the methods will depend on the acid strength and the
oxidizing or reducing powers of the solutions. The extraction mixture of 4.0 N nitric
acid plus 0.7 N hydrocloric acid at 90°C is certainly the strongest acidic and oxidizing
mixture other than the total extraction method. Therefore it is expected that all
adsorbed metals, precipitated salts, oxides and hydroxides of iron and manganese and
most organically complexed metals would be extracted. Weak hydrochloric acid will
remove loosely bonded and adsorbed metals, precipitated salts, and possibly attack
some of the less resistant silicates such as layered silicates. Both 4.0 N nitric acid plus
0.7 N hydrochloric acid and 0.5 N hydrochloric acid may attack some silicates. This,
in addition to the more effective extractions, has resulted in the higher mean values
shown in Table 2.14.
Of the three major elements studied, aluminium and iron are mainly found in the
aluminosilicate crystal lattice. Only a small portion of manganese is found in this
phase. This is confirmed in Fig. 2.3 a where the distribution of manganese along the
river is essentially the same with all five extraction methods. This means that they are
all attacking the same phase of manganese in the sediment. Figure 2.3 b and Table 2.14, however, show that only the total and 4.0 N nitric acid plus 0.7 N hydrochloric acid methods extract the bulk of iron and aluminium respectively.
The three weaker methods show only a very small percentage of the total iron and
aluminium extracted, with the same uniform distribution along the river. This indica-
River and Stream Sediments
(d) As in (b) but digested in 100 ml of 1 N hydroxylamine hydrochloride plus 25 %
acetic acid solution.
(e) As in (b) but digested in 100 ml of 0.05 N EDTA solution of pH 4.8.
Fig. 2.2 a-g presents the levels of cadmium, copper, lead, zinc, nickel, chromium and
cobalt along the river, using the four partial extraction methods, together with a total
extraction method involving Parr bomb digestion. For cadmium, the total and 4.0 N
nitric acid plus 0.7 N hydrochloric acid levels were not obtained because the small
sample size used in these methods did not provide enough metal in solution to give a
detectable signal. The anomalous regions are visually quite apparent in spite of the
small number of samples used, cadmium, copper, lead, zinc, and nickel showing very
well defmed anomalies with all methods. For chromium this is less clear, while no
significant anomalies are seen for cobalt. Fig. 2.3 a-c provide similar data for iron,
manganese and aluminium. These three are major elements and they have no significant anomalies. All methods, except the total and 4.0 N Nitric acid plus 0.7 N hydrochloric acid, provide the same type of anomalies and the same distribution of metal levels
along the river. This means that the three weaker extraction methods (0.5 N hydrochloric acid, 1 N NHpH·HCI plus 25 % acetic acid and 0.5 N EDTA) attacked essentially the
same part of the sediment. The other two methods showed the same type of distribution
as the three weaker methods only in the cases of copper, lead, zinc, nickel and manganese. The absolute amount of metal extracted decreases as the extracting solution becomes weaker. Of the partial extraction methods, the 4.0 N nitric-hydrochloric acid
solution is highest followed by the 0.5 N hydrochloric acid solution. The amount of
metal extracted by the other two weaker solutions, relative to each other, depends on
the metal involved. Table 2.14 shows the mean background levels of each metal in the
Rideau River sediments calculated by excluding the anomalous samples.
The extracting efficiency of the methods will depend on the acid strength and the
oxidizing or reducing powers of the solutions. The extraction mixture of 4.0 N nitric
acid plus 0.7 N hydrocloric acid at 90°C is certainly the strongest acidic and oxidizing
mixture other than the total extraction method. Therefore it is expected that all
adsorbed metals, precipitated salts, oxides and hydroxides of iron and manganese and
most organically complexed metals would be extracted. Weak hydrochloric acid will
remove loosely bonded and adsorbed metals, precipitated salts, and possibly attack
some of the less resistant silicates such as layered silicates. Both 4.0 N nitric acid plus
0.7 N hydrochloric acid and 0.5 N hydrochloric acid may attack some silicates. This,
in addition to the more effective extractions, has resulted in the higher mean values
shown in Table 2.14.
Of the three major elements studied, aluminium and iron are mainly found in the
aluminosilicate crystal lattice. Only a small portion of manganese is found in this
phase. This is confirmed in Fig. 2.3 a where the distribution of manganese along the
river is essentially the same with all five extraction methods. This means that they are
all attacking the same phase of manganese in the sediment. Figure 2.3 b and Table 2.14, however, show that only the total and 4.0 N nitric acid plus 0.7 N hydrochloric acid methods extract the bulk of iron and aluminium respectively.
The three weaker methods show only a very small percentage of the total iron and
aluminium extracted, with the same uniform distribution along the river. This indica-