Publication Date:
2019-07-17
Description:
In order to analyse differences in concentration, speciation
and total mobility of arsenic two different locations were
studied near the Helgoland Mud Area, North Sea.
The first location is characterised by natural
sedimentation, the second by deposited sediments dredged
from the port of Hamburg. Porewater as well as sediment
profiles were analysed with respect to arsenic compounds (As
(III) and total As) and major redox species as total and
reactive manganese and iron. The sediment samples were
handled under inert atmosphere before and during extraction
by water, phosphate, hydrochloric acid and aqua regia. Total
element contents in porewater and leachable extracts of
sediment fractions were analysed.
The results show a strong redox coupling of arsenic with
manganese and iron. Oxidized arsenic seems to adsorb to
manganese- and iron-oxyhydroxides in surface sediments. In
contrast to the solid samples, the pore water data shows a
release of As (III) into porewater when manganese- and ironoxyhydroxides
are reduced in the upper part of the cores. Also
a remobilisation of As (V) occurs. Downward diffusing
arsenic can be fixed by carbonate below the zone of
manganese and iron reduction. In the anoxic parts of the
sediments As (III) and As (V) are released and could be fixed
at authigenic iron sulphide or arsenic sulphides formation. A
sulfidic precipitation of arsenic in iron-dominated systems is
limited by the occurrence of HS-.
Total solid-phase contents in leachable extracts of
sediment fractions of the natural area show significant higher
arsenic concentrations than the core of the anthropogenic
dumping area. This is due to the higher fines content of the
Helgoland mud area.
Higher total porewater contents of iron and arsenic in the
core of the anthropogenic dumping area thus due to higher
turnover rates of organic matter by iron reduction. Higher
concentrations of arsenic may be due to a higher availability
of iron in the dumped sediments.
Repository Name:
EPIC Alfred Wegener Institut
Type:
Article
,
notRev
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