499
DNA damage. In conclusion, we attempt to compare the endpoints, assess the sensitivity and utility, and link molecular- and individual-level impacts to larger population and community-level effects.
29.2 Test Organism Sensitivity
29.2.1 Species-Specific Differences in Sensitivity to Oil
Exposure
Parallel studies, using identical WAF preparations and exposure conditions, of acute
toxicity to larval fish have revealed substantial differences among species (McKim
et al. 1985) underscoring the range of sensitivities in different species and the
importance of selecting the optimal test organism. In these studies of acute toxicity,
7-day-old inland silverside (Menidia beryllina) was more sensitive than 3-day-old
sheepshead minnow (Cyprinodon variegatus) and more sensitive than <1-day-old
Gulf killifish (Fundulus grandis) (Finch et al. 2017). These apparent differences in
sensitivity should be viewed in the context of the age of the test organisms. Age, and
presumably size, confers a higher tolerance to acute exposures to oil as illustrated
on studies of bay anchovy exposed to HEWAF preparations of Macondo oil. These
24-h exposure studies on bay anchovy established LC50 values of 9.71 μg/L TPAH
for embryos, compared to 690 and 1610 μg/L TPAH for 5- and 21-day-old larvae,
respectively (Duffy et al. 2016; O’Shaughnessy et al. 2018). Thus, the observation
that older silverside are more sensitive than the newly hatched killifish further
underscores the significant difference in sensitivity among organisms. Although
other factors may be at play, sensitivity differences among species may be a reflection of differences in PAH metabolism. In a DWH oil intraperitoneal injection (IP)
study assessing species-specific PAH metabolism differences of subadult red drum
(Sciaenops ocellatus), Florida pompano (Trachinotus carolinus), and southern
flounder (Paralichthys lethostigma), analysis of PAH bile metabolites indicated that
pompano exhibited a much faster rate of PAH metabolism than red drum and southern flounder. Results suggest that pompano may be better able to depurate toxic
PAH compounds (Pulster et al. 2017).
29.2.2 Differences in Sensitivity Among Life Stages
Early life stages are generally more sensitive to environmental insults than older
conspecifics which form the foundation for acceptance of early life stage toxicity
testing as a faster and more cost-effective alternative to full life-cycle tests. In most
cases, early life stage testing accurately predicts outcomes of full life-cycle tests
(McKim 1985). Size is undoubtedly an important factor determining differences in
29 Digging Deeper than LC/EC50: Nontraditional Endpoints and Non-model Species…
DNA damage. In conclusion, we attempt to compare the endpoints, assess the sensitivity and utility, and link molecular- and individual-level impacts to larger population and community-level effects.
29.2 Test Organism Sensitivity
29.2.1 Species-Specific Differences in Sensitivity to Oil
Exposure
Parallel studies, using identical WAF preparations and exposure conditions, of acute
toxicity to larval fish have revealed substantial differences among species (McKim
et al. 1985) underscoring the range of sensitivities in different species and the
importance of selecting the optimal test organism. In these studies of acute toxicity,
7-day-old inland silverside (Menidia beryllina) was more sensitive than 3-day-old
sheepshead minnow (Cyprinodon variegatus) and more sensitive than <1-day-old
Gulf killifish (Fundulus grandis) (Finch et al. 2017). These apparent differences in
sensitivity should be viewed in the context of the age of the test organisms. Age, and
presumably size, confers a higher tolerance to acute exposures to oil as illustrated
on studies of bay anchovy exposed to HEWAF preparations of Macondo oil. These
24-h exposure studies on bay anchovy established LC50 values of 9.71 μg/L TPAH
for embryos, compared to 690 and 1610 μg/L TPAH for 5- and 21-day-old larvae,
respectively (Duffy et al. 2016; O’Shaughnessy et al. 2018). Thus, the observation
that older silverside are more sensitive than the newly hatched killifish further
underscores the significant difference in sensitivity among organisms. Although
other factors may be at play, sensitivity differences among species may be a reflection of differences in PAH metabolism. In a DWH oil intraperitoneal injection (IP)
study assessing species-specific PAH metabolism differences of subadult red drum
(Sciaenops ocellatus), Florida pompano (Trachinotus carolinus), and southern
flounder (Paralichthys lethostigma), analysis of PAH bile metabolites indicated that
pompano exhibited a much faster rate of PAH metabolism than red drum and southern flounder. Results suggest that pompano may be better able to depurate toxic
PAH compounds (Pulster et al. 2017).
29.2.2 Differences in Sensitivity Among Life Stages
Early life stages are generally more sensitive to environmental insults than older
conspecifics which form the foundation for acceptance of early life stage toxicity
testing as a faster and more cost-effective alternative to full life-cycle tests. In most
cases, early life stage testing accurately predicts outcomes of full life-cycle tests
(McKim 1985). Size is undoubtedly an important factor determining differences in
29 Digging Deeper than LC/EC50: Nontraditional Endpoints and Non-model Species…