474
G.E. Glass et al.
bags, and the precleaning of all sampling equipment. Both the Ekman dredge and
the piston corer were rinsed with on-site water several times before and after
each sample was taken. Clean techniques were also used for subsampling and
analysis of the Lake Superior core.
All other materials such as gloves, larger ziploc bags, measuring utensils, and
glassware were tested for mercury contamination by soaking for 1 to 4 days in a
solution made of a dichromate/nitric acid preservative and distilled water.
Mercury concentrations in the soak solutions were found to be below the total
mercury detection limit «2 ng/l) in water.
2.3
Analyses Methods
2.3.1
Mercury in Sediment
Analyses for mercury concentrations in sediment were conducted using cold
vapor atomic absorption spectrometry (CVAA) according to USEPA (1991)
method 245.5 with minor modifications (Glass et al. 1990). Samples were analyzed
wet and in some cases as wet and dried pairs. All results are reported on a dry
weight basis. Instrument calibration was accomplished using three laboratory
working standards (60, 180, and 540 ng Hg/I) and two reagent blanks at the
beginning and end of each analytical run.
Sediment samples were thoroughly mixed by kneading the ziploc bag for up to
5 min followed by stirring the contents with a spatula before removing an aliquot
from the bag for analysis. Aliquots were placed directly into analysis flasks and
weighed. In addition, a separate aliquot was transferred to a crucible for percent
moisture determination.
2.3.2
Mercury in Benthos
Analyses for mercury concentrations in benthos were conducted using USEP A
(1991) method 245.6 with minor modifications (Glass et al. 1990). Between 7 and
75 mg of dried (105°C overnight) benthos tissue was used per analysis.
Instrument calibration was performed at the beginning and end of each
analytical run using three laboratory working standards (15, 30, and 60 ng HgJl)
and two reagent blanks. Analytical precision was approximated by analyzing
similar organisms (species and size) from the same sampling site. All results are
reported on a dry weight basis.
G.E. Glass et al.
bags, and the precleaning of all sampling equipment. Both the Ekman dredge and
the piston corer were rinsed with on-site water several times before and after
each sample was taken. Clean techniques were also used for subsampling and
analysis of the Lake Superior core.
All other materials such as gloves, larger ziploc bags, measuring utensils, and
glassware were tested for mercury contamination by soaking for 1 to 4 days in a
solution made of a dichromate/nitric acid preservative and distilled water.
Mercury concentrations in the soak solutions were found to be below the total
mercury detection limit «2 ng/l) in water.
2.3
Analyses Methods
2.3.1
Mercury in Sediment
Analyses for mercury concentrations in sediment were conducted using cold
vapor atomic absorption spectrometry (CVAA) according to USEPA (1991)
method 245.5 with minor modifications (Glass et al. 1990). Samples were analyzed
wet and in some cases as wet and dried pairs. All results are reported on a dry
weight basis. Instrument calibration was accomplished using three laboratory
working standards (60, 180, and 540 ng Hg/I) and two reagent blanks at the
beginning and end of each analytical run.
Sediment samples were thoroughly mixed by kneading the ziploc bag for up to
5 min followed by stirring the contents with a spatula before removing an aliquot
from the bag for analysis. Aliquots were placed directly into analysis flasks and
weighed. In addition, a separate aliquot was transferred to a crucible for percent
moisture determination.
2.3.2
Mercury in Benthos
Analyses for mercury concentrations in benthos were conducted using USEP A
(1991) method 245.6 with minor modifications (Glass et al. 1990). Between 7 and
75 mg of dried (105°C overnight) benthos tissue was used per analysis.
Instrument calibration was performed at the beginning and end of each
analytical run using three laboratory working standards (15, 30, and 60 ng HgJl)
and two reagent blanks. Analytical precision was approximated by analyzing
similar organisms (species and size) from the same sampling site. All results are
reported on a dry weight basis.