Passive dosing yields dissolved aqueous exposures of crude oil comparable to the CROSERF (Chemical Response to Oil Spill: Ecological Effects Research Forum) water accommodated fraction method

Abstract

The Chemical Response to Oil Spill: Ecological Effects Research Forum's water accommodated fraction procedure was compared with 2 alternative techniques in which crude oil was passively dosed from silicone tubing or O-rings. Fresh Macondo oil (MC252) was dosed at 30 mg/L using each approach to investigate oil dissolution kinetics, which was monitored by fluorometry as estimated oil equivalents (EOEs). Subsequent experiments with each dosing method were then conducted at multiple oil loadings. Following equilibration, test media were analytically characterized for polyaromatic hydrocarbons (PAHs) using gas chromatography (GC)-mass spectrometry and dissolved oil using biomimetic solid-phase microextraction (SPME). The results showed that equilibrium was achieved within 72 h for all methods. Measured PAH concentrations were compared with oil solubility model predictions of dissolved exposures. The concentration and composition of measured and predicted dissolved PAHs varied with oil loading and were consistent between dosing methods. Two-dimensional GC compositional data for this oil were then used to calculate dissolved toxic units for predicting MC252 oil acute toxicity across the expected range of species sensitivities. Predicted toxic units were nonlinear with loading and correlated to both EOE and biomimetic SPME. Passive dosing methods provide a practical strategy to deliver and maintain dissolved oil concentrations while avoiding the complicating role that droplets can introduce in exposure characterization and test interpretation. Environ Toxicol Chem 2018;37:2810-2819. © 2018 SETAC.

Oil toxicity test methods must be improved

“…Passive dosing for static test solutions is equivalent to the partition‐controlled delivery of a single PAC by equilibrium partitioning from polydimethylsiloxane (silicone) films (e.g., Kiparissis et al ; Lin et al ). For oil solutions, passive dosing systems include silicone tubing filled with oil (Redman et al ) or silicone O‐rings soaked in oil (Bera et al ). Hydrocarbons partition from oil to silicone and from silicone to water when the silicone media are immersed in water with constant stirring (Redman et al ).…”

“…Passive dosing appears technically simpler than continuous‐flow technologies and requires less oil. Times to equilibria and the concentrations of oil transferred to water compared favorably with WAF solutions produced by stirring water and oil for up to 72 h (Bera et al ). For all passive dosing systems, test solutions should be analyzed frequently to describe changes in composition as the more water‐soluble and degradable components are depleted (Organisation for Economic Co‐operation and Development ), and to detect the release of oil droplets (Redman et al ).…”

“…As an alternative, Redman and Parkerton () recommend passive sampling devices to accumulate dissolved hydrocarbons from water, and oil partitioning models to estimate the bioavailable fraction from K OW of individual compounds. In combination with models of pharmacokinetics and toxic units, this biomimetic solid‐phase microextraction of test solutions can reduce errors in estimated toxicity when oil concentrations change over time (Letinski et al ; Bera et al ). This approach has also shown that low molecular weight soluble hydrocarbons contribute more to acute lethality than larger compounds (Redman and Parkerton ).…”

“…This approach has also shown that low molecular weight soluble hydrocarbons contribute more to acute lethality than larger compounds (Redman and Parkerton ). A similar approach has been applied to chronic toxicity using average acute to chronic ratios (Bera et al ) but validation is needed with actual chronic toxicity tests.…”

Determining the water solubility of difficult-to-test substances: A tutorial review

“…Another method is to dose through liquid filled tubes. This method has been demonstrated using two oils and stirring of either the water phase [56] or stirring of the oil filled silicone tubing tied to the stir bar at 300 rpm [57]. The method is however vulnerable to production of micro-emulsions [42] and leakage from the ends of the tubing [46].…”