Anions in seawater - Determination of Anions in Natural and Treated Waters - page 364

others, hydrated iron(II) oxide served as both reductant and carrier. Ishibashi and
Shigematsu [44] used co-precipitation with aluminium hydroxide and did not employ
reduction, so that the value reported most likely corresponds to inorganic chromium(III)
alone; in fact, the present value for inorganic chromium(III) is in remarkable agreement.
In Chuecas and Riley's study [45] the samples were stored for a long time under acidic
conditions before analysis, so that chromium(VI) could have been reduced to chromium
(III) and any organic chromium dissociated with the result that all chromium species
would have been determined as chromium(III). When a sample is reduced under acidic
conditions, organic chromium is likely to dissociate partly, initially increasing the
apparent concentration of chromium(VI). When the analytical procedure described earlier
[46,47] was re-examined the value for chromium(III) was found actually to be the sum of
chromium(III) and chromium(VI) while the value for chromium(VI) was partly organic
chromium. For the same reason the chromium(VI) values determined by Fukai [48],
Fukai and Vas [49] and Yamamoto et al. [50] probably include organic chromium
species. When an iron(II) precipitate is used, there seems to be little chance of
determining the organic chromium species as chromium(VI). The value for chromium
(VI) reported by Cranston and

Table 3.4 Literature data on the chromium contents of seawater

Ref. Date Locations Methods Concentration

µg L −1

Al(OH) 3 co ppt

Ishibashi and
Shigematsu [44]

1950 Japanese coastal Cr(III),

0.01

Fe(OH) 3 co ppt
acidic reduction

Chuecas and
Riley [45]

1966 British coastal Cr(III) 0.46

Cr(VI)0.01

Fe(OH) 3 coppt
acidic reduction

Fukai [48,49] 1967 Mediterranean Cr(III) 0.02-0.25

Cr(VI) 0.05-0.38

BiOH (NO 3 ) 2
co ppt acidic
reduction

Cr(III)? Cr(III) +
Cr(IV) 0.1 3-0.90
Cr(VI)? OrgCr
0.07-0.27

Kuwamoto
and Murai [46]

1970 Pacific Ocean

Fe(OH) 3 co ppt
Fe(OH) 3 reduction

Grimaud and
Michard [47]

1974 Pacific Ocean Cr(III) 0.24-0.52

Cr(VI) 0.03-0.11

Al(OH) 3 co ppt
acidic reduction

Yamamoto et al. [50] 1974 Pacific Ocean Total 0.06-0.96

Cr(III) 17-99%

Fe(OH) 3 co ppt Fe(OH) 3 reduction

Cr(III) 0.005
Cr(VI) 0.15

Cranston and
Murray [35]

1978 Pacific Ocean

Nakayama et al. [38] 1981 Pacific Ocean

and Japan Sea

Cr(III) 0.06
Cr(IV) 0.14
OrgCr 0.26