Controls on metal exposure to aquatic organisms in urban streams

Abstract

Streams in urban ecosystems receive metal inputs primarily from stormwater runoff and wastewater effluent. The relative contribution of these metal sources to stream impairment is difficult to discern based on simple water characteristics and biological surveys. Stream impairment in these systems is often indicated by reduced abundance and diversity of aquatic insects, which tend to be more sensitive to chronic metal exposures. Metal species and controls on metal species in both the waterborne and dietborne exposure pathways to aquatic organisms are reviewed here. In addition, ecological changes that can control dietborne species are discussed. A main focus is on how organic matter from different anthropogenic sources may control both aqueous metal speciation as well as interaction with various inorganic or microbiological surfaces in streams. Most of the reviewed research focuses on Cu, Zn or Pb as those are the primary metals of concern in developed systems and Cu and Pb have unique and strong interactions with organic matter. Recommendations for further research are described in the context of exposure species, dynamics of exposure, stoichiometry, or advanced analytical tools, and regulatory implications are discussed.

Trophic Strategies Influence Metal Bioaccumulation in Detritus-Based, Aquatic Food Webs

“…For instance, urbanization has led to changes in DOC composition with concurrent increases in both DOC lability, , and metal binding capacity . In addition to changes in land cover, warming and shifting hydrologic regimes can impact the quantity and quality of DOC entering streams. , Changes in DOC composition may diminish the mitigating effects of DOC, and could make the microbial loop a more significant pathway for metal accumulation in urban streams, where metals tend to be more abundant and metal pollution has been shown to negatively influence ecological processes. , This may be especially true in systems that were naturally dominated by filter-feeding species, such as black flies. Future work related to the microbial loop and metal accumulation would benefit from characterizing the metal binding characteristics of the DOC used, as this potentially confounds effects of lability in laboratory studies.…”

Ligand Steric Interactions Modulate Multidentate Ligand Exchange Pathways: Kinetics of Nickel(II) Ion Capture from N-Substituted IDA Complexes by CDTA

“…In aquatic environments, the speciation of solubilized transition-metal ions is predominated by complexes with in situ multidentate ligands (e.g., metallophores, 1 synthetic chelating agent contaminants, 2,3 natural organic matter 4 ). 5,6 Speciation is far from equilibrium due to the slow kinetics of multidentate ligand exchange reactions…”

“…In aquatic environments, the speciation of solubilized transition-metal ions is predominated by complexes with in situ multidentate ligands (e.g., metallophores, synthetic chelating agent contaminants, , natural organic matter). , Speciation is far from equilibrium due to the slow kinetics of multidentate ligand exchange reactions where M is the metal ion, and both L and Y are multidentate ligands (charges, protonation, and bound water molecules are omitted here for simplicity). ,,, The stepwise dissociation of relatively stable initial complexes, ML, during multidentate ligand exchange can produce very low rates of reaction. Furthermore, time scales of these reactions vary by many orders of magnitude as the rate-determining step shifts due to factors including steric interactions, ligand structure, ligand/complex rigidity, ligand protonation, electrostatic interactions, and electronic effects. − …”