Establishing cause–effect relationships in hydrocarbon-contaminated sediments using a sublethal response of the benthic marine alga, Entomoneis CF Punctulata

Abstract

A sublethal whole-sediment toxicity test that uses flow cytometry to measure inhibition of esterase activity in the marine microalga Entomoneis cf punctulata was applied to the assessment of hydrocarbon-contaminated sediments and toxicity identification and evaluation (TIE). Concentration-response relationships were developed, and a 20% effect concentration for total polycyclic aromatic hydrocarbons (PAHs) of 60 mg/kg normalized to 1% total organic carbon was calculated. Relationships between toxic effects and sediment organic carbon concentrations, organic carbon forms (e.g., black carbon), and sediment particle size indicated that further normalization of hydrocarbon concentrations to sediment particle size may improve concentration-response relationships. The algal toxicity test was applied as a rapid whole-sediment TIE procedure that involved the addition to sediment of powdered coconut charcoal (PCC), a hydrophobic, carbon-based material that strongly adsorbs PAHs and decreases the pore-water exposure pathway. Sediments with PCC concentrations of up to 15% (w/w) provided acceptable responses in control sediments. For six sediments with total PAH concentrations of 1,060, 4,060, 5,120, 9,150, 9,900, and 15,900 mg/kg, inhibition of E. cf punctulata esterase activity (% of control) was 75, 97, 94, 93, 100, and 97%, respectively. Following a 15% PCC amendment to these sediments, inhibition of esterase activity was 0, 1, 11, 69, 32, and 68%, respectively, indicating a decrease in toxicity in all sediments. Because the alga E. cf punctulata is exposed to toxicants via both pore water and overlying water, the reduction in toxicity achieved by 15% PCC additions can be related to the efficient removal of dissolved hydrocarbons released from sediment particles. The sediment-PCC manipulations coupled with algal whole-sediment toxicity tests provided an effective and rapid TIE method to determine whether hydrocarbon contaminants are responsible for toxicity in sediments.

A short life-cycle test with the epibenthic copepod Nitocra spinipes for sediment toxicity assessment

“…Survival, with an EC10 of 256 mg Cu/L, was the least sensitive endpoint. The results indicated that N. spinipes is of comparable sensitivity to other species commonly used for whole-sediment toxicity test procedures [5,27]. Considering copepod species, Bengtsson [14] reported an LC50 value for N. spinipes survival of 1,800 mg Cu/L, which is five times greater than the value of 347 mg Cu/L obtained in the present study.…”

“…Dissolved ammonia was analyzed colorimetrically using a Merck Spectroquant Kit (14752). Analyses of organics were made according to United States Environmental Protection Agency (U.S. EPA) standard methods [26] as described previously [27]. The limits of reporting for the various methods were less than 1/10th of the lowest reported values.…”

Application of surrogate methods for assessing the bioavailability of PAHs in sediments to a sediment ingesting bivalve

“…Procedures for sediment size fractionation (63 µm sieves), total organic carbon (TOC by high temperature TOC analyser) and speciation of organic carbon into biogenic/diagenetic organic carbon (OC, loss on ignition at 375 ºC) and combustion-derived black carbon (BC, loss on ignition at 1050 ºC) forms have been described previously (Simpson et al, 2006). Analyses of total petroleum hydrocarbons (TPHs) followed USEPA methods 8260/8015 (USEPA, 1996).…”

Reviews of Environmental Contamination and Toxicology

“…A whole-sediment and water-only toxicity test was developed for algae based upon inhibition of esterase activity, with results showing sensitivity to copper and sediment particles (copper tailings) (Adams and Stauber 2004). Follow-up studies in which Entomoneis cf punctulata was exposed to hydrocarbon-contaminated sediments showed this assay to have efficacy (Simpson et al 2007). These authors recommended the use of algal esterase activity as a wholesediment TIE method to determine the contribution of hydrocarbon contamination to sediment toxicity.…”