Phototoxic target lipid model of single polycyclic aromatic hydrocarbons

Abstract

A phototoxic target lipid model (PTLM) is developed to predict phototoxicity of individual polycyclic aromatic hydrocarbons (PAHs) measured either as median lethal concentration (LC50) or median lethal time (LT50) for a 50% toxic response. The model is able to account for the differences in the physical/chemical properties of PAHs, test species sensitivities, and variations in light source characteristics, intensity, and length of exposure. The PTLM is based on the narcotic target lipid model (NTLM) of PAHs. Both models rely on the assumption that mortality occurs when the toxicant concentration in the target lipid of the organism reaches a threshold concentration. The PTLM is applied to observed LC50s and LT50s for 20 individual PAHs, 15 test species-including arthropods, fishes, amphibians, annelids, mollusks, and algae-exposed to simulated solar and various UV light sources, for exposure times varying from less than 1 h to 100 h, a total of 333 observations. The LC50 concentrations range from less than 0.1 µg/L to greater that 10 µg/L. The model has 2 fitting parameters that are constant and apply to all PAHs and organisms. The root mean square errors of prediction for log(LC50) and log(LT50) are 0.473 and 0.382, respectively. The results indicate that the PTLM can predict the phototoxicity of single PAHs over a wide range of exposure conditions and to organisms with a wide range of sensitivities. Environ Toxicol Chem 2017;36:926-937. © 2016 SETAC.

Evaluation of the phototoxicity of unsubstituted and alkylated polycyclic aromatic hydrocarbons to mysid shrimp (Americamysis bahia): Validation of predictive models

“…In the present study, nonphototoxic compounds had the highest HOMO-LUMO gap of all compounds tested. Phototoxicity is dependent on the lipid body burden [33], and therefore, this may be an unaccounted factor that increased the toxicity of alkylated PAHs in the present study. The addition of methyl groups to PAHs increases the lipophilicity of the compound [32], most likely increasing the lipid body burden in the organism.…”

Predicting phototoxicity of alkylated PAHs, mixtures of PAHs, and water accommodated fractions (WAF) of neat and weathered petroleum with the phototoxic target lipid model

“…A PTLM was developed to predict the acute phototoxicity of single PAHs . The PTLM predicts the increase in toxicity relative to the narcotic toxicity where PLC50 is the phototoxic median lethal concentration (mmol/L) that produces 50% mortality in the presence of light (phototoxicity), NLC50 is the narcotic LC50 (mmol/L; Equation ), P abs (mol photon/mol PAH) is the quantity of photons absorbed by PAHs, and a and R '* are the equation constants (0.426 ± 0.037 and 0.510 ± 0.097, respectively).…”

“…The term converts the incident light I o ( λ ) in units of W/m 2 /nm to moles photons/m 3 /s, which, when multiplied by time T exp (s), yields moles of incident photons/m 3 during the light exposure time. The dimensional analysis of P abs can be found in the Supplemental Data, S13, of Marzooghi et al .…”

“…Compositional information and aqueous concentrations of each WAF sample, including all oil types (MASS, CTC, and Juniper ) and all WAF dilutions (100, 25, and 6.25%), are reported in the Supplemental Data, Worksheet 1. For each component, when the reported concentration exceeded the corresponding aqueous solubility, S , it was assumed that the concentration at which organisms were exposed is the aqueous solubility . That is, if C w, i > S i , then C w, i = S i was used.…”

A critical review of polycyclic aromatic hydrocarbon phototoxicity models

“…The dashed lines represent 1 order of magnitude uncertainties. (From Marzooghi et al , reprinted with permission. )…”