Environmental Sampling Techniques - Fundamentals of Environmental Sampling and Analysis - page 92

4.2.5 Biological Sampling
Biological sampling rests on the responsibility of trained ecologist or biologist. In
Section 4.1.5, we discussed very briefly on the sampling tools for biota samples used
in chemical residual analysis. In addition to residual analysis, biota sampling may be
aimed at toxicological testing on contaminated sediment and surface water, or even
community response assessment based on sampling results from terrestrial
vegetation, benthic organisms, or fish, to just name a few. Readers in this
specialized area should consult the detailed guidelines by the U.S. EPA, APHA, and
the USGS provided at the end of this chapter (APHA, 1998; USGS 1993a-e).
Practical tips
Biological samples are not easy to collect in many cases. Insufficient sample
size due to the lack of specimen availability could result in an invalid
statistical inference.
If an improper biota sampling protocol was implemented, data may later find
to be flawed. Causes could be the neglect of vast size differences between
species, variations with a study population, tissue differentiations, growth
stage, and habitat.
Biological samples are noted for being much more susceptible to the
decomposition of organic analytes than are other types.
4.2.6 Air and Stack Emission Sampling
Common types of air samples include ambient (outdoor) air, indoor or workplace air,
and air from stacks or other types of emission exhausts such as automotive exhausts.
Soil air is sometimes collected for special purpose such as from landfills or
Superfund sites. Ambient air sampling represents two critical challenges. First, the
concentrations for most atmospheric pollutants in ambient are very low. The analysis
of low level organic compounds in the air requires large sample volumes. Second,
the large variations in analyte concentrations can occur within in a short period of
time due to the meteorological effects. Ambient air samples should be collected at a
location that most closely approximates the actual human exposure.
Indoor air sampling requires some special considerations (Keith, 1991). The
ventilation systems due to heating or cooling equipment can alter air flow and add
pollutants to the air. The location of a sampler within a room will influence the
results obtained. Household chemicals (cleaning agents, pesticides) could add
compounds to the air that must be documented and considered.
Sampling air in a duct or a stack is another matter entirely. The location should
be approximately three-quarters of the way down a long, straight run of ductwork
(Bodger, 2003). The flow will be relatively calm in such a location and, as a result,
the sample is more representative. For stationary sources such as stack emission, the
sampling site and the number of traverse points used for the collection affect the
quality of the data. Depending on the stack geometry, a cross-section of the stack