Freshwater salinization is an emerging global problem impacting safe drinking water, ecosystem health and biodiversity, infrastructure corrosion, and food production. Freshwater salinization ...originates from diverse anthropogenic and geologic sources including road salts, human-accelerated weathering, sewage, urban construction, fertilizer, mine drainage, resource extraction, water softeners, saltwater intrusion, and evaporative concentration of ions due to hydrologic alterations and climate change. The complex interrelationships between salt ions and chemical, biological, and geologic parameters and consequences on the natural, social, and built environment are called Freshwater Salinization Syndrome (FSS). Here, we provide a comprehensive overview of salinization issues (past, present, and future), and we investigate drivers and solutions. We analyze the expanding global magnitude and scope of FSS including its discovery in humid regions, connections to human-accelerated weathering and mobilization of ‘chemical cocktails.’ We also present data illustrating: (1) increasing trends in salt ion concentrations in some of the world’s major freshwaters, including critical drinking water supplies; (2) decreasing trends in nutrient concentrations in rivers due to regulations but increasing trends in salinization, which have been due to lack of adequate management and regulations; (3) regional trends in atmospheric deposition of salt ions and storage of salt ions in soils and groundwater, and (4) applications of specific conductance as a proxy for tracking sources and concentrations of groups of elements in freshwaters. We prioritize FSS research needs related to better understanding: (1) effects of saltwater intrusion on ecosystem processes, (2) potential health risks from groundwater contamination of home wells, (3) potential risks to clean and safe drinking water sources, (4) economic and safety impacts of infrastructure corrosion, (5) alteration of biodiversity and ecosystem functions, and (6) application of high-frequency sensors in state-of-the art monitoring and management. We evaluate management solutions using a watershed approach spanning air, land, and water to explore variations in sources, fate and transport of different salt ions (
e.g.
monitoring of atmospheric deposition of ions, stormwater management, groundwater remediation, and managing road runoff). We also identify tradeoffs in management approaches such as unanticipated retention and release of chemical cocktails from urban stormwater management best management practices (BMPs) and unintended consequences of alternative deicers on water quality. Overall, we show that FSS has direct and indirect effects on mobilization of diverse chemical cocktails of ions, metals, nutrients, organics, and radionuclides in freshwaters with mounting impacts. Our comprehensive review suggests what could happen if FSS were not managed into the future and evaluates strategies for reducing increasing risks to clean and safe drinking water, human health, costly infrastructure, biodiversity, and critical ecosystem services.
Freshwater salinization syndrome (FSS) refers to the suite of interactive effects of salt ions on degradation of physical, biological, and social systems. Best management practices (BMPs), which are ...methods to effectively reduce runoff and nonpoint source pollution (stormwater, nutrients, sediments), do not typically consider management of salt pollution. We investigate impacts of FSS on mobilization of salts, nutrients, and metals in urban streams and stormwater BMPs by analyzing original data on concentrations and fluxes of salts, nutrients, and metals from 7 urban watersheds in the Mid-Atlantic USA and synthesizing literature data. We also explore future critical research needs through a survey of practitioners and scientists. Our original data show 1) sharp pulses in concentrations of salt ions and metals in urban streams directly following both road salt events and stream restoration construction (e.g., similar to the way concentrations increase during other soil disturbance activities); 2) sharp declines in pH (acidification) in response to road salt applications because of mobilization of H+ from soil exchange sites by Na+; 3) sharp increases in organic matter from microbial and algal sources (based on fluorescence spectroscopy) in response to road salt applications, likely because of lysing cells and changes in solubility; 4) substantial retention (~30–40%) of Na+ in stormwater BMP sediments and floodplains in response to salinization; 5) increased ion exchange and mobilization of diverse salt ions (Na+, Ca2+, K+, Mg2+), nutrients (N, P), and trace metals (Cu, Sr) from stormwater BMPs and restored streams in response to FSS; 6) downstream increasing loads of Cl–, SO42–, Br–, F–, and I– along flowpaths through urban streams and P release from urban stormwater BMPs in response to salinization; and 7) a substantial annual reduction (>50%) in Na+ concentrations in an urban stream when road salt applications were dramatically reduced, which suggests potential for ecosystem recovery. We compare our original results with published metrics of contaminant retention and release across a broad range of stormwater BMPs from North America and Europe. Overall, urban streams and stormwater BMPs consistently retain Na+ and Cl– but mobilize multiple contaminants based on salt types and salinity levels. Finally, we present our top 10 research questions regarding FSS impacts on urban streams and stormwater BMPs. Reducing diverse chemical cocktails of contaminants mobilized by freshwater salinization is a priority for effectively and holistically restoring urban waters.
Factors driving freshwater salinization syndrome (FSS) influence the severity of impacts and chances for recovery. We hypothesize that spread of FSS across ecosystems is a function of interactions ...among five state factors: human activities, geology, flowpaths, climate, and time. (1) Human activities drive pulsed or chronic inputs of salt ions and mobilization of chemical contaminants. (2) Geology drives rates of erosion, weathering, ion exchange, and acidification‐alkalinization. (3) Flowpaths drive salinization and contaminant mobilization along hydrologic cycles. (4) Climate drives rising water temperatures, salt stress, and evaporative concentration of ions and saltwater intrusion. (5) Time influences consequences, thresholds, and potentials for ecosystem recovery. We hypothesize that state factors advance FSS in distinct stages, which eventually contribute to failures in systems‐level functions (supporting drinking water, crops, biodiversity, infrastructure, etc.). We present future research directions for protecting freshwaters at risk based on five state factors and stages from diagnosis to prognosis to cure.
The mechanism for catalysis of DNA alkylation by the potent antitumor antibiotic duocarmycin SA (DSA) has been probed by determining the structure of a DNA adduct of the indole analogue (DSA-indole, ...DSI) lacking three methoxy functional groups. The three-dimensional structure of DSI covalently bound to A19 in d-(G1ACTAATTGAC11)·d-(G12TCAATTAGTC22) was determined by 1H NMR spectroscopy using a total of 935 experimental distance and dihedral angle constraints. The representative ensemble of 20 conformers has no distance restraint violations greater than 0.03 Å, no torsional restraint violations greater than 0.7°, and a pairwise rmsd over all atoms in the binding site of 0.48 Å. Comparison of the structures of the DSA and DSI adducts reveals a structural basis for the critical role of one of the trimethoxy-indole functional groups in alkylation reactivity. A deeper penetration into the DNA minor groove in the vicinty of the indole subunit is observed for the DSI versus the DSA adduct, along with some variations in the width and depth of the minor groove throughout the binding site. The most significant difference between the DSI and DSA addducts is the 8° smaller twist of the two ligand subunits in DSI, which correlates with its ∼20-fold slower rate of DNA alkylation. This comparison of the structures of the DSI and DSA adducts to the same DNA duplex provides the most direct evidence to date in support of the proposal that the binding of the ligand in the DNA minor groove and consequent twisting of the two ligand subunts, disrupting vinylogous amide stabilization and thereby activating the conjugated cyclopropane electrophile, plays a central role in controlling DNA alkylation reactivity.
The three-dimensional solution structure of duocarmycin SA in complex with d-(G
1ACTAATTGAC
11)·d-(G
12TCATT
A
GTC
22) has been determined by restrained molecular dynamics and relaxation matrix ...calculations using experimental NOE distance and torsion angle constraints derived from
1H NMR spectroscopy. The final input data consisted of a total of 858 distance and 189 dihedral angle constraints, an average of 46 constraints per residue. In the ensemble of 20 final structures, there were no distance constraint violations >0.06 Å or torsion angle violations >0.8°. The average pairwise root mean square deviation (RMSD) over all 20 structures for the binding site region is 0.57 Å (average RMSD from the mean: 0.39 Å). Although the DNA is very
B -like, the sugar-phosphate backbone torsion angles β, ϵ, and ζ are distorted from standard values in the binding site region. The structure reveals site-specific bonding of duocarmycin SA at the N3 position of adenine 19 in the AT-rich minor groove of the duplex and binding stabilization
via hydrophobic interactions. Comparisons have been made to the structure of a closely related complex of duocarmycin A bound to an AT-rich DNA duplex. These results provide insights into critical aspects of the alkylation site selectivity and source of catalysis of the DNA alkylating agents, and the unusual stability of the resulting adducts.
Duocarmycin SA is a member of a growing class of interesting lead compounds for chemotherapy, distinguished by the manner in which they bind to and react with DNA substrates. The first ...three-dimensional structure of a DNA adduct of an unnatural enantiomer from this family has been determined by 1H NMR methods. Comparison to the previously determined structure of the natural enantiomer bound in the same DNA-binding site provides unique insights into the similarities and critical distinctions producing the respective alkylation products and site selectivities. The results also support the hypothesis that the duocarmycin SA alkylation reaction is catalyzed by the binding to DNA, and provide a deeper understanding of the structural basis for this unique mode of activation.
We report the NMR solution structure of (+)-CPI-indole (CPI, 1,2,8,8a-tetrahydrocyclopropacpyrrolo3,2-eindol-4(5H)-one), an agent belonging to the CC-1065/duocarmycin family of antitumor compounds. ...This (+)-CPI-indole structure is covalently bound to d(G₁ACTAATTGTC₁₁)-d(G₁₂TCAATTAGTC₂₂), a synthetic DNA duplex containing a high-affinity binding site. The three-dimensional structure has been determined by several cycles of restrained molecular dynamics calculations with a total of 563 NMR-derived constraints, both in vacuo and by using the generalized Born solvent continuum model. In-depth analysis of the structure of this ligand-DNA complex led to a detailed knowledge of the bound state conformation of the CPI-indole, the most simplified agent related to CC-1065 and duocarmycins, the parent members of a family of extremely potent antitumor compounds. Comparison of the CPI-indole bound conformation with those previously found for (+)-duocarmycin SA (DSA), its unnatural enantiomer (−)-DSA, and the demethoxylated analogue (+)-DSI in their DNA complexes provided additional evidence of the tight correlation between the catalytic effect exerted by DNA on the alkylation reaction and the extent of angular twist between the two planar heteroaromatic subunits of these agents. Additionally, comparison of the structural features of the DNA-bound state of a “naked” ligand, such as CPI-indole, with those of various other duocarmycin agents provided useful information for the interpretation of the observed effects on chemical reactivity of the different substitution patterns at the hemispheres of these types of complex.
Precise connections between race, poverty, and the condition of America's cities are drawn in this collection of seventeen essays. Policymakers and scholars from a variety of disciplines analyze the ...plight of the urban poor since the riots of the 1960s and the resulting 1968 Kerner Commission Report on the status of African Americans. In essays addressing health care, education, welfare, and housing policies, the contributors reassess the findings of the report in light of developments over the last thirty years, including the Los Angeles riots of 1992. Some argue that the long-standing obstacles faced by the urban poor cannot be removed without revitalizing inner-city neighborhoods; others emphasize strategies to break down racial and economic isolation and promote residential desegregation throughout metropolitan areas. Guided by a historical perspective, the contributors propose a new combination of economic and social policies to transform cities while at the same time improving opportunities and outcomes for inner-city residents. This approach highlights the close links between progress for racial minorities and the overall health of cities and the nation as a whole. The volume, which began as a special issue of the North Carolina Law Review , has been significantly revised and expanded for publication as a book. The contributors are John Charles Boger, Alison Brett, John O. Calmore, Peter Dreier, Susan F. Fainstein, Walter C. Farrell Jr., Nancy Fishman, George C. Galster, Chester Hartman, James H. Johnson Jr., Ann Markusen, Patricia Meaden, James E. Rosenbaum, Peter W. Salsich Jr., Michael A. Stegman, David Stoesz, Charles Sumner Stone Jr., William L. Taylor, Sidney D. Watson, and Judith Welch Wegner. |Precise connections between race, poverty, and the condition of America's cities are drawn in this collection of 17 essays. Policymakers and scholars from a variety of disciplines analyze the plight of the urban poor since the riots of the 1960s and the resulting 1968 Kerner Commission Report on the status of African Americans. In essays addressing health care, education, welfare, and housing policies, the contributors reassess the findings of the report in light of developments over the last thirty years, including the Los Angeles riots of 1992. Guided by a historical perspective, the contributors propose a new combination of economic and social policies to transform cities while at the same time improving opportunities and outcomes for inner-city residents.
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