Environmental Engineering Reference
In-Depth Information
2.2
Sediments
Until now, most analytical methods have been developed for water samples
and less attention has been paid to sediments. In this sense, less survey data
is available concerning the occurrence of biocides in sediments. Reported con-
centrations of biocides that have been found in sediments are at the low ng g -1
level [14, 35, 37, 38]. Extraction from sediments has been developed with con-
ventional and current techniques. Recovery results for different extraction
methods are shown in Tables 1 and 2. LLE is usually preformed by shaking
or sonication [14, 34-36]. DCM, acetone or a mixture of both is commonly
selected as the organic solvent. For the cleanup step, deactivated Florisil is typ-
ically used as the adsorbent. With this procedure, the recoveries are satisfactory
( > 82%) for compounds such as Irgarol 1051 [14], Chlorothalonil [14, 35], and
Dichlofluanid [14, 34, 35]. Similar recoveries ( > 80%) have been also obtained
for Diuron from sediments, for which most extraction methods have only been
based on LLE and sonication [50, 52, 53]. Soxhlet extraction is also applied but
only with volatile organic solvents (acetone). The extraction efficiency of this
technique was lower for Irgarol 1051 [37] with recoveries of 61%.
SFE has been evaluated as an approach to minimize solvent usage and
compared to conventional extraction techniques for its validation [38]. Pa-
rameters such as pressure and temperature have moderate effects on extrac-
tion efficiency, while the modifier content in CO 2 is significant. SFE of Irgarol
1051 is feasible with CO 2 modified with 20% methanol in the presence of TFA
(0.65 M in MeOH). The reported recoveries of Irgarol 1051 are similar to those
obtained with conventional extraction techniques (87%) [38].
In general, satisfactory recovery values have been reported when cur-
rent extraction techniques have been applied. With SPME for sediments,
the efficiency of extraction is comparable to the results in water samples.
So, for example, Irgarol showed a 90% recovery using a coated fibre of
PDMS-DVB [26]. In this study, the use of extraction solvents with differ-
ent polarity (water, methanol, acetone and acetonitrile) was also evaluated.
The best results were obtained with acetone while with water, the recoveries
decreased to 66%. This effect was observed for the extraction of Chloro-
tahlonil, Dichlofluanid and Sea-nine 211 decreasing to the range 30-37%,
using water [26].
As an alternative to conventional extraction methods, MAE has been as-
sessed for the extraction of Irgarol 1051 and its main degradation product
M1. This technique is based on the adsorption of microwave energy by ex-
traction solvents, which results in an increase of temperature and pressure.
In this way, diffusion of the compounds from the sediments to the solvent
can be achieved. The presence of water in the sediments can be a benefit in
the MAE technique, given that it helps non-polar organic solvents to absorb
the microwave energy. In addition, the use of water was found to be a satis-
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