Effects-based spatial assessment of contaminated estuarine sediments from Bear Creek, Baltimore Harbor, MD, USA

Abstract

Estuarine sediments in regions with prolonged histories of industrial activity are often laden to significant depths with complex contaminant mixtures, including trace metals and persistent organic pollutants. Given the complexity of assessing risks from multi-contaminant exposures, the direct measurement of impacts to biological receptors is central to characterizing contaminated sediment sites. Though biological consequences are less commonly assessed at depth, laboratory-based toxicity testing of subsurface sediments can be used to delineate the scope of contamination at impacted sites. The extent and depth of sediment toxicity in Bear Creek, near Baltimore, Maryland, USA, was delineated using 10-day acute toxicity tests with the estuarine amphipod Leptocheirus plumulosus, and chemical analysis of trace metals and persistent organic pollutants. A gradient of toxicity was demonstrated in surface sediments with 21 of 22 tested sites differing significantly from controls. Effects were most pronounced (100% lethality) at sites proximate to a historic industrial complex. Sediments from eight of nine core samples to depths of 80 cm were particularly impacted (i.e., caused significant lethality to L. plumulosus) even in locations overlain with relatively non-toxic surface sediments, supporting a conclusion that toxicity observed at the surface (top 2 cm) does not adequately predict toxicity at depth. In seven of nine sites, toxicity of surface sediments differed from toxicity at levels beneath by 28 to 69%, in five instances underestimating toxicity (28 to 69%), and in two instances overestimating toxicity (44 to 56%). Multiple contaminants exceeded sediment quality guidelines and correlated positively with toxic responses within surface sediments (e.g., chromium, nickel, polycyclic aromatic hydrocarbon (PAH), total petroleum hydrocarbon). Use of an antibody-based PAH biosensor revealed that porewater PAH concentrations also increased with depth at most sites. This study informs future management decisions concerning the extent of impact to Bear Creek sediments, and demonstrates the benefits of a spatial approach, relying primarily on toxicity testing to assess sediment quality in a system with complex contaminant mixtures.

Evaluating porewater polycyclic aromatic hydrocarbon–related toxicity at a contaminated sediment site using a spiked field‐sediment approach

“…The particular location of sediment collection within Bear Creek was approximately 2 km north of the region of primary contaminant introduction and has served as an "in-system" reference sediment with !90% survival in previous 10-d acute toxicity tests (Hartzell et al 2017;McGee et al 2004McGee et al , 1999. The second sediment, referred to as "cove sediment," was collected from Bigwood Cove on the Wye River, MD, USA, an area with no history of industrial activity and low concentrations of PAHs, PCBs, and metals (Hartzell et al 2017). Specifically, the harbor sediment was fine-grained (silty-clay), with a high fraction of organic carbon (f oc ¼ 0.056 dry wt) and high porewater content (76% by weight).…”

“…In addition to mixtures of PAHs, sediments in estuarine environments are often enriched with many other classes of contaminants. However, given the complex nature of sediment contamination, it can often be difficult to link classes of compounds to observed biological effects, especially when multiple contaminant classes correlate with toxic responses (D evier et al 2011;Gauthier et al 2014;Hartzell et al 2017). Identifying a primary contaminant(s) of concern at impacted sites is necessary for sound decision-making concerning environmental management and remediation.…”

“…Sediments within Bear Creek are elevated in PAHs, polychlorinated biphenyls (PCBs), and organochlorine pesticides (Ashley and Baker 1999;Hartwell and Hameedi 2007), as well as heavy metals including zinc, chromium, copper, and lead (Ashley and Baker 1999;Mason et al 2004;Hartzell et al 2017). Studies of sediment toxicity in Bear Creek, performed over the past 2 decades, have demonstrated persistent acute lethality to benthic organisms (McGee et al 2004(McGee et al , 1999Hartzell et al 2017), with the highest toxicity observed in sediments collected nearest historical sources of industrial activity and diminishing lethality with increasing distances from industrial activity (Hartzell et al 2017). Concurrent chemical analysis on sediments used in toxicity tests identified multiple and diverse contaminants, many of which correlated with observed toxicity and with one another, which made assigning causality impossible and limited the ability to predict effects elsewhere in the system based solely on chemical analysis (Hartzell et al 2017;Pourabadehei and Mulligan 2016).…”

“…Studies of sediment toxicity in Bear Creek, performed over the past 2 decades, have demonstrated persistent acute lethality to benthic organisms (McGee et al 2004(McGee et al , 1999Hartzell et al 2017), with the highest toxicity observed in sediments collected nearest historical sources of industrial activity and diminishing lethality with increasing distances from industrial activity (Hartzell et al 2017). Concurrent chemical analysis on sediments used in toxicity tests identified multiple and diverse contaminants, many of which correlated with observed toxicity and with one another, which made assigning causality impossible and limited the ability to predict effects elsewhere in the system based solely on chemical analysis (Hartzell et al 2017;Pourabadehei and Mulligan 2016). Toxicity may be principally the consequence of one contaminant class or the result of multiple contaminant stressors interacting.…”

“…Moreover, contributions to toxicity may come from mixtures of contaminants from the same class (e.g., complex PAHs) or from multiple distinct contaminant classes (i.e., metals and persistent organics; Swarz et al 1995;Hagopian-Schlekat et al 2001;Hedfi et al 2013). However, multiple other compounds, including PCBs, total petroleum hydrocarbon (TPH), chromium, and nickel, were also positively correlated with mortality (Hartzell et al 2017). In a recent study of Bear Creek sediments, mortality of test organisms was found to weakly positively correlate with PAHs in both porewater (R 2 ¼ 0.45, p ¼ 0.03) and whole sediment (R 2 ¼ 0.47, p ¼ 0.025).…”