Determine the potential for sediments and associated porewaters to abiotically degrade pesticides and other contaminants;Identify the responsible reductants that catalyze these reactions;Determine the rates of pesticide degradation for a given set of redox parameters;Identify and determine the products from these reactions.; andModel the results in a manner that will allow coastal zone managers (CZMs) to best exploit this process for managing water quality in Lake Erie.

Wetlands may provide a means of managing nonpoint source pollution since water from diffuse sources can collect in wetland basins before final discharge. While some pollutants will be degraded by sunlight (see RP/S-22 and 29) and by microbial pathways in the water column, others will be sequestered in sediments. These sediments may have very active chemical constituents that can potentially degrade these pesticides. Thus, the questions that need to be asked are: 1) Which pesticides are susceptible to such degradative pathways? 2) How quickly can these pesticides breakdown? 3) What are the responsible natural reductants in sediments? and 4) What products are formed from such processes? By supporting this research we will be able to delineate between those pesticides that will ultimately be degraded in coastal wetland sediments, and those that will simply accumulate and remain a threat for future generations.

We will obtain intact sediment cores from Old Woman Creek (OWC), some of which will be sectioned under argon, while others will be squeezed anoxically (using specially designed squeezers) to expel the porewaters. We will use a number of agricultural pesticides that will specifically react with reductants to form derivatives of known structure. These compounds will also react rapidly enough to preclude microbial processes, even though sterile or poisoned controls will be conducted in parallel. This will aid us in elucidating 1) the responsible reductant, 2) the relative reductive potential of the sediment, and 3) the type and reactivity of the derivatives that are formed. The reaction rates and derivatives from the reaction will be carefully measured and the results used to develop simple, but robust kinetic models of the degradation process.Reaction premixtures (with and without oxidized NOM) containing 28 mM MOPS buffer were prepared outside the glovebox, purged with argon, and Fe(II) and C6Cl5NO2 added inside the glovebox. All reactions were performed in glass syringes with no headspace, and reaction aliquots quenched with 2N HCl in 4 mL glass vials. High performance liquid chromatography (HPLC) was used to identify C6Cl5NO2 and its reaction product pentachloroaniline (C6Cl5NH2). Fe(II) and FeT were measured colorimetrically, and [DOC] measured with a Shimadzu TOC 5000. Particle count analyses were performed with a Brookhaven Instruments Particle Size Analyzer.Natural wetland porefluids were extracted from sediments collected at Old Woman Creek in northern Ohio. Sediment cores were collected from the wetland in plastic coring tubes, and transferred to a Jahnke-type core squeezer (18). Porefluids were squeezed from nitrogen-purged ports into ground glass syringes, and combined according to depth sections within the sediment core to average core-specific spatial heterogeneity. Aliquots for Fe and DOM concentration analyses were separated from combined porefluids and acidified, and reactions were performed by adding C6Cl5NO2 stock for a target [C6Cl5NO2] =1.0 mM.

We found complete reduction of C6Cl5NO2 to C6Cl5NH2 in clean system reaction media containing both Fe(II) and DOM, and no reduction in DOM-only reaction media (Figure 1). These data showed that Fe(II) was necessary for reduction to occur, and we assumed that reduction obeyed pseudo-first order kinetics due to the exponential decrease of [C6Cl5NO2] over time.   The formation of the C6Cl5NHOH intermediate was observed as reported by Klupinski et al. (2004), and other intermediates were assumed not to be major components of the reduction (9). In modeling reaction kinetics, we assumed that C6Cl5NHOH is the primary intermediate, where kA is the limiting reaction step and t represents time (eqn 1 & 2): Generally, Fe(II)-only control reactions were faster than Fe(II)-DOM reactions.   We performed particle count analyses of our clean system reaction media in order to determine 1) if particles were present during the reduction of C6Cl5NO2, and; 2) if particles increased during the course of the reaction. Results from reaction media-normalized particle count analyses show an increase in particle counts for the Fe(II)-only system, and no change in both Fe(II)-PLFA and Fe(II)-SRFA systems (Figure 2). The Fe(II)-only slope is positive (162.4 min-1), while both Fe(II)-DOM slopes are negative (-27.96 min-1 and -69.59 min-1 for Fe(II)-PLFA and Fe(II)-SRFA reactions, respectively).{No benefits or accomplishments entered, please replace this text with content.}