Project ID Assignment - MFW-3: Decoupling and Recoupling Plant-Herbivore
Systems to Determine the Fate and Impact of Nanomaterials in Freshwater
Environments
Research team:
Ed McCauley, Roger Nisbet, Louise Stevenson, Helen Dickson
Ecological systems are dynamically coupled populations, composed of individuals
of different species acquiring resources, expending energy, and cycling materials. Novel
chemical nanomaterials (NM) introduced to environments could significantly alter any
or all of these fundamental processes (Baun et al., 2008 Ecotoxicology; Hartmann et al.,
2010 Toxicology; Petersen et al., 2009 Environ. Sci. Technol.) leading to changes in major
features of population dynamics, including persistence (van der Ploeg et al., 2011
Environ. Pollut.). A major challenge is to predict the effects of these novel
nanomaterials in environments of interacting populations, or more broadly how the
dynamics of coupled populations change as we move from one “environment” to
another. There is evidence of trophic transfer (Bouldin et al., 2008 Environ. Toxicol.
Chem.; Ferry et al., 2009 Nat. Nanotechn.; Holbrook et al., 2008 Nat. Nanotechnol.; Zhu
et al., 2010 Chemosphere) and even bioaccumulation of nanomaterials in bacterial
(Werlin et al., 2011 Nat. Nanotechnol.) and terrestrial systems (Judy et al., 2011 Enviro.
Sci.Technol.).
The challenge is made harder because the fate and transport of these NM’s are
largely unknown in many environments, and chemical and biological characteristics of
natural systems can alter the behavior and thus toxicity of NMs, rendering classical
exposure concepts potentially ineffective (Baun et al., 2008 Ecotoxicology; Christian et
al., 2008 Ecotoxicology; Klaine et al., 2008 Environ. Sci. Technol.).
There are (at least) two missing components to address this challenge: 1) an
experimental system that we can use to investigate the dynamical implications of
exposure to NM and to understand how changes in major system properties emerge in
the presence of NM as they move through the environment, and 2) a quantitative
framework that can be used both to identify causal mechanisms producing these
responses and to generalize these results to different ecological systems and
environments.
We have developed these components for freshwater plankton systems, where
we have a tight linkage between models at key levels of biological organization and real
dynamical experimental systems (McCauley et al. 2008 Nature, Nelson et al. 2006
Nature, McCauley et al. 1999 Nature). Our models successfully predict the
presence/absence of complex dynamical behavior as we change major environmental
variables, such as temperature or the availability of major nutrient resources (McCauley
et al. in prep, LaMontagne et al. in prep). Mechanisms controlling the equilibria and
stability of these systems have been independently tested, using novel experiments that
measure requisite individual responses in dynamically interacting populations. Our
theories accurately capture these dynamics in systems without NMs ranging from
milliliters to kiloliters, thereby enabling us to study impacts of NMs over a wide range of
spatial scales.
With this tight coupling between models and experimental systems, we hope to
provide insight into the vexing problem of assessing both direct and indirect effects of
NMs. The direct effects on simple individual and population parameters are hard to
assess, given problems in establishing exposure levels and evaluating toxicity or
mechanisms of action (Klaine et al., 2008 Environ. Sci. Technol.). However, concurrently
evaluating indirect effects manifested through subsequent feedback of processes that
could compensate or magnify direct effects seems like fantasy. We think we can
accomplish this difficult assessment through the use of novel dynamic experiments,
where we will systematically “decouple” then “recouple” resource-consumer
interactions in the absence and presence of NMs in parallel replicate environments. At
the same time, performance of individuals will be assessed to assist in the interpretation
of the causal mechanisms being altered by exposure to NM’s (c.f .Nisbet et al. 2010
Phil.Trans.Royal Soc., Nisbet et al. 2004 Ecology) and to explore HTS
approaches. Finally, the information on the performance of individuals will be used to
derive model predictions for the effects of NM on the dynamics of our predator-prey
system, and these predictions will be evaluated against the results from the decoupledcoupled semi-chemostat experiments.
Our initial experiments use batch culture conditions followed by a continuous
flow system, but the approach will be expanded in years 2 and 3 to include larger-scale
systems with richer microbial processes. We have completed testing the effect citratecoated silver nanoparticles on a bacterial-algal system in batch culture and in semichemostat conditions. There are tremendous opportunities for collaboration with
ongoing research in Fate, transport and life cycle analysis and Terrestrial ecosystems
impact and hazard assessment that we have begun to take advantage of and look
forward to continued collaboration in the future. McCauley has built and equipped an
aquatic lab at UCSB designed to complete experiments ranging from microcosms
through to mesocosms. He has invested in state-of-the art equipment for the
automated analysis of freshwater systems that will provide the rich data-stream needed
to monitor dynamics at all levels of biological organization. Other labs in the UC CEIN
have also utilized this equipment for analysis of other nanoparticle experiments. The
comparison of results from comparable freshwater and marine microcosms and
mesocosms in our research group will provide insight into how major environmental
factors modify fate and impact in these resource-consumer systems. Other experiments
focused on the effects of silver nanoparticles on marine algae are currently being
conducted in the Lenihan lab in the CEIN. To our knowledge, our experiments will serve
as the first data on the effects of citrate-coated silver nanoparticles on algae or Daphnia,
and one of few experiments investigating the effects of nanoparticles on a dynamic
system. Further, the setup and design of the sequence of experiments described in the
previous paragraph is novel in the field.