It's the Dose, Not the Hypothesis: Reply to Heintz et al. (2014)

Dear Editor, The basis for ecotoxicology is the relationship between dose and response. Hypothesis testing can be indicative of difference, but should never be relied on without considering whether there is a true dose-response relationship. Hypothesis testing cannot inform the researcher regarding causation or uncertainty associated with an observed response, particularly in the case of complex exposures. We (Page et al. 2012a) evaluated experiments conducted by Heintz et al. (1999) and Carls et al. (1999) that assessed the toxicity of petroleum to developing pink salmon and herring embryos. The results of these experiments, based on hypothesis testing, were reported as evidence of toxicological effects from exposure to 1 μg/L or lower of dissolved total polycyclic aromatic hydrocarbons (TPAH), and as evidence that oil toxicity increased with weathering. Our evaluation was not, as Heintz et al. (2014) incorrectly stated, focused on “supposed failure to adequately control exposure levels” in the experiments. Although we found a number of issues with the work as reported that led us to question the certitude of the conclusions reached, our main focus was on the lack of a dose-response relationship in those experiments rather than on the hypothesis testing relied on by Heintz et al. (1999) and Carls et al. (1999). We found that these two articles and the articles that followed, which relied on these initial studies, did not provide technically defensible causal evidence for TPAH toxicity at 1 μg/L or lower (the toxicity benchmark was at least an order of magnitude higher), nor that oil toxicity increased with weathering. Below we provide responses to all of the concerns raised by Heintz et al. (2014) regarding our evaluations of their earlier work (Page et al. 2012a,b,c; Landrum et al . 2012, 2013; Neff et al. 2013). We (Landrum et al. 2012) previously congratulated Heintz, Carls, and co-workers “for providing more data and information for analysis than other papers that evaluated toxicological responses to time-varying concentrations of individual compounds or complex mixtures.” We again congratulate them for their pioneering work, but respectfully request that they fully consider the evidence we present, which is not “speculative misinterpretation.” Their interpretation of their findings, based on hypothesis testing, was not unreasonable as a preliminary analysis. However, with further consideration, particularly of the lack of dose-response relationships, and of the continuing failure to establish cause and effect, we find their interpretation is not technically defensible without corroborative testing. Such corroborative testing has not been reported (see below); in fact,