Geoscience Reference
In-Depth Information
research vessel) of atmospheric contaminants and avoiding any surface layers of the water
body under study (see
Section 4.2.4
). Always record any potential sources of contamina-
tion when collecting samples in the field.
Second, careless handling is a major source of contamination including working in a
dirty environment, careless sampling procedures, and not wearing disposable gloves. Any
water that enters the sample bottle should not have been in contact with either a gloved or
a bare hand, and latex gloves should be avoided as they can leach absorbing compounds.
Powderless polypropylene or nitrile gloves are recommended. Careless sample handling
is easily avoided by the investigator, and gloves should be worn at all times; however,
working in a dirty environment (e.g., muddy wetlands) is common for many investigators.
One simple solution is to employ the clean hands/dirty hands approach as outlined by the
U.S. Geological Survey (U.S. Geological Survey,
2006
) if two people are available. Briefly
stated, one person is designated as clean hands (CH) and one person as dirty hands (DH)
and both wear disposable gloves. CH is responsible for all operations involving equipment
that comes into contact with the sample (e.g., changing filters), whereas DH is responsible
for all operations involving contact with potential sources of contamination (e.g., preparing
sampling equipment such as pumps; handling of equipment such as multiparameter instru-
ments for ancillary field measurements). Another alternative if working in a dirty environ-
ment is to set up a clean workspace (e.g., in a clean laboratory on a research vessel or inside
a vehicle) where sample processing can be carried out without further undue exposure to
potential contaminants.
Finally, the sampling equipment itself may represent a source of contamination.
Leaching of organic substances from new plastics as well as the sorption of organics to
some plastics means that some fluorocarbon polymers, polypropylene, polyethylene (lin-
ear), polyvinyl chloride, silicone, and nylon sampling equipment are not recommended for
DOM work (Lane et al.,
2003
). Nylon tubing in particular has been shown to leach absorb-
ing compounds (
Figure 4.1
) and so is to be avoided. Glass, Teflon, and some “aged” plastic
containers are recommended when cleaned appropriately (see
Section 4.2.3
). Metals such
as stainless steel are appropriate (e.g., pressure filtration unit) if not corroded and cleaned
appropriately. It is strongly recommended that all sampling equipment be blank checked
with laboratory grade water (preferably type I ultrapure water, 18.2 MΩ cm
-1
at 25°C with
DOC < 10 ppb) at each step of possible contamination.
4.2.2 Blanks and Replicate Samples
The easiest way to catch any potential contamination issues is through the use of appro-
priate blanks utilizing laboratory-grade water. Blanks can address a range of issues as
highlighted by the U.S. Geological Survey (
2006
). For example, field blanks should be
collected and processed at the field site in exactly the same way as the samples of interest,
replacing the sample water with laboratory grade water. This allows an overall contamina-
tion effect of all the collection and processing to be observed and represents a basic quality
control on the whole sampling design. This can then be broken down into subcomponents
