76
Pesticides, Organic Contaminants, and Pathogens in Air
Chambers for microcosm studies can vary in design (i.e., open or closed,
shape, size) depending on the research needs/goals. For example, studies
to monitor the microbial dechlorination of vinyl chloride, a carcinogen, in
contaminated groundwater have been performed in small 160 mL serum
bottles with vinyl chloride introduced to the headspace and monitored for
the non-chlorinated degradation products (Findlay et al., 2016). By contrast,
studies of aerobic microbial cometabolic degradation of trichloroethylene
with toluene were performed in semicontinuous slurry microcosms that contained soil and water from a contaminated site (Han et al., 2007). Finally,
studies to monitor the microbial degradation of petroleum hydrocarbons in
contaminated soil have been performed in soil-flled columns through which
air was passed to promote oxidation of the hydrocarbons by the microbes
(Schaffner et al., 1998). The results of these microcosm studies were used to
develop remediation strategies for contaminated ecosystems (see, for example, work done by GZA GeoEnvironmental, Inc.).
A chamber model that has been used for pesticide environmental fate
studies is Metcalf’s aquatic/terrestrial farm pond microcosm (Metcalf et al.,
1971). This model was generally composed of a glass aquarium containing
sand, water, and plants. It has been referred to as “an Illinois farm pond in a
box,” a quote attributed to Metcalf. The sand–water system contained snails,
water feas, algae, and plankton. After the system reached equilibrium, the
plants were dosed with a solution containing a radiolabeled chemical. This
construct allowed him to document meticulously, precisely, and with repeatability the movement of pesticides through the trophic web. Metcalf and his
coworkers evaluated over 200 chemicals in this terrestrial–aquatic ecosystem, providing invaluable information on the environmental suitability not
only of pesticides but also of industrial chemicals such as polychlorinated
biphenyls and animal supplements. Information obtained from this model
ecosystem, and others like it, confrmed information obtained laboriously
from decades of feld studies, validating the method as a fast, inexpensive,
and reliable index of environmental fate.
Another study involving a pesticide was the assessment of the sensitivity of freshwater organisms—invertebrates and algae—to the fungicide fuazinam in single-species laboratory tests and together in microcosms (Van
Wijngaarden et al., 2010). The study showed that a measure of species sensitivity was the same for the microcosm communities as in the single-species
tests, showing the utility of the microcosm approach.
5.3.2 Empirical Models (Mesocosm)
Mesocosms are somewhat in-between “real-world conditions” and the artifcial confnes of a laboratory chamber, but with less control over variables
(Table 5.1). Mesocosms can vary in size and complexity, depending on the
research needs. One document describes a mesocosm design for pesticide
registration efforts (Touart, 1980). The design calls for a pond of about 0.1 acres
Pesticides, Organic Contaminants, and Pathogens in Air
Chambers for microcosm studies can vary in design (i.e., open or closed,
shape, size) depending on the research needs/goals. For example, studies
to monitor the microbial dechlorination of vinyl chloride, a carcinogen, in
contaminated groundwater have been performed in small 160 mL serum
bottles with vinyl chloride introduced to the headspace and monitored for
the non-chlorinated degradation products (Findlay et al., 2016). By contrast,
studies of aerobic microbial cometabolic degradation of trichloroethylene
with toluene were performed in semicontinuous slurry microcosms that contained soil and water from a contaminated site (Han et al., 2007). Finally,
studies to monitor the microbial degradation of petroleum hydrocarbons in
contaminated soil have been performed in soil-flled columns through which
air was passed to promote oxidation of the hydrocarbons by the microbes
(Schaffner et al., 1998). The results of these microcosm studies were used to
develop remediation strategies for contaminated ecosystems (see, for example, work done by GZA GeoEnvironmental, Inc.).
A chamber model that has been used for pesticide environmental fate
studies is Metcalf’s aquatic/terrestrial farm pond microcosm (Metcalf et al.,
1971). This model was generally composed of a glass aquarium containing
sand, water, and plants. It has been referred to as “an Illinois farm pond in a
box,” a quote attributed to Metcalf. The sand–water system contained snails,
water feas, algae, and plankton. After the system reached equilibrium, the
plants were dosed with a solution containing a radiolabeled chemical. This
construct allowed him to document meticulously, precisely, and with repeatability the movement of pesticides through the trophic web. Metcalf and his
coworkers evaluated over 200 chemicals in this terrestrial–aquatic ecosystem, providing invaluable information on the environmental suitability not
only of pesticides but also of industrial chemicals such as polychlorinated
biphenyls and animal supplements. Information obtained from this model
ecosystem, and others like it, confrmed information obtained laboriously
from decades of feld studies, validating the method as a fast, inexpensive,
and reliable index of environmental fate.
Another study involving a pesticide was the assessment of the sensitivity of freshwater organisms—invertebrates and algae—to the fungicide fuazinam in single-species laboratory tests and together in microcosms (Van
Wijngaarden et al., 2010). The study showed that a measure of species sensitivity was the same for the microcosm communities as in the single-species
tests, showing the utility of the microcosm approach.
5.3.2 Empirical Models (Mesocosm)
Mesocosms are somewhat in-between “real-world conditions” and the artifcial confnes of a laboratory chamber, but with less control over variables
(Table 5.1). Mesocosms can vary in size and complexity, depending on the
research needs. One document describes a mesocosm design for pesticide
registration efforts (Touart, 1980). The design calls for a pond of about 0.1 acres