Environmental Engineering Reference
In-Depth Information
3
Partitioning and Fate in Sediments
The fate of alternative biocides in the aquatic environment is closely linked
to their partitioning between aqueous media and particulate matter and
sediment. The partitioning depends upon physicochemical parameters dic-
tated by water chemistry and geographical considerations. Factors include
sediment characteristics, presence of suspended sediment and the chemical
characteristics of the water column [75] and the specific characteristics of the
areasampled,forexamplethevolumeoftheharbour[50].
Organic pollutants can either be sorbed onto particulate matter or exist in
solution. Adsorption onto particulate matter and flocculation—in which the
species are trapped by newly formed particulate matter—are often termed
as “sorption” [21]. Sorption is responsible for reducing both the concentra-
tion and the toxicity of biocides in the water column, and is also the principal
pathway for accumulation in sediments.
Influences on the transfer of Irgarol, chlorothalonil, dichlofluanid and di-
uron from the soluble to the particulate phase in estuarine environments
have been investigated [76]. For these four biocides the removal from wa-
ter increases with the concentration of particulate matter. The sorption of
chlorothalonil and dichlofluanid is enhanced at high pH (8.0) and increased
suspended matter, whilst for Irgarol and diuron the influence of pH is not
obvious. Salinity does not seem to play a significant role in the partition-
ing behaviour of the biocides. Comparisons of different sediment types show
that silty-clay sediments exhibit a larger capacity for biocide adsorption than
silty-sandy sediments. There are clearly different patterns of sorption for each
biocide as controlled by the physicochemical environment.
Sediment disturbances may release biocides back into the water column.
Where the initial sediment concentrations of the biocides are low, the con-
centrations in water, resulting from desorption, are below detection lim-
its. Dichlofluanid is among the most strongly bound to sediments, with
a release of less than 1%(0.6-0.9%) from contaminated sediments. Irgarol
and chlorothalonil demonstrate a higher degree of desorption (1.9-2.4 and
1.2-1.7%, respectively) [76].
3.1
Irgarol
Irgarol has been shown to have strong adsorption characteristics [77]. It
has been detected in marine sediments in Greece [78] Germany [50], the
UK [52], Spain [79] and Sweden [80] and in freshwater sediments in Lake
Geneva [44].
Irgarol levels in sediment after the boating season are significantly higher
than those before and after the boating season and levels of Irgarol in
