Role of Reduced Sulfur Species in Promoting the Transformation of Triazines in Estuaries and Salt MarshesEPA Grant Number: R826269
Title: Role of Reduced Sulfur Species in Promoting the Transformation of Triazines in Estuaries and Salt Marshes
Investigators: Roberts, A. Lynn , Salmun, H.
Institution: The Johns Hopkins University
EPA Project Officer: Hiscock, Michael
Project Period: February 1, 1998 through January 31, 2001 (Extended to January 31, 2002)
Project Amount: $304,163
RFA: Exploratory Research - Environmental Chemistry (1997) RFA Text | Recipients Lists
Research Category: Water , Land and Waste Management , Air , Engineering and Environmental Chemistry
Existing data are inadequate to enable accurate prediction of the persistence of triazines and closely related compounds (widely used as herbicides and dye constituents) in coastal environments. We hypothesize that reactions with certain reduced sulfur species present in estuaries and salt marshes could exert a significant impact on rates of removal of such contaminants. Although prior studies have demonstrated that reduced sulfur species can serve as important environmental nucleophiles through reactions with halogenated aliphatic compounds, very little is known of the rates at which they engage in nucleophilic aromatic substitution with susceptible substrates. Providing the necessary data is the principal objective of this research. Some of the products of these reactions may be of environmental significance; hence, an additional goal is to investigate their ability to bind covalently to natural organic matter. Finally, the impact reduced sulfur species could exert on the fate of contaminants in estuaries and salt marshes will be briefly examined through a dynamic box model approach.
Rates of reaction of reduced sulfur species with chlorinated triazines (and closely-related compounds) will be determined in well-defined systems. Variables will include concentrations of reduced sulfur species and pH so that second-order rate constants for each sulfur species-contaminant pair can be obtained. Additional experiments will be conducted using the more complex matrix of natural sulfidic waters to test our understanding of the governing processes. The ability of reduced sulfur moieties present in natural organic matter to enhance the removal of triazines will be determined in careful kinetic experiments; complementary studies will be conducted with 13C and 14C-labeled substrates to investigate the type and permanence of binding. The results of the kinetic experiments will be used to develop a dynamic multibox model that factors in the interplay between the physics of a typical coastal system (specifically, rates of mixing between fresh and sulfidic waters) and the chemistry. This model will be used to simulate the behavior of triazines in order to provide preliminary evaluation of the potential significance of these removal processes.
The data generated will help in assessing the fate of a major class of contaminants (including information that may be related to the ability of salt marshes to treat effect their removal). The results should be useful to EPA for regulation of textile dye waste discharges and for establishing scientifically-based limits on herbicide usage in coastal areas.