Effects of Early Life exposure to the Organophosphate Flame Retardant, Triphenyl Phosphate on Stress and Stress Related Behaviour in Birds

Our environment is contaminated by hundreds of thousands of chemicals. While regulations have been established to control production and release of some of these chemicals, thousands of new chemicals are introduced to the market on an annual basis. Traditional toxicity tests have focused on outcomes such as mortality, impaired growth and reproduction. However, recent studies have been promoting behaviour as a measure of exposure to contaminants, given that it is more sensitive than traditional toxicological endpoints, can encompass multiple levels of biological organization, and is directly related to an organism’s fitness. Among other effects, it alters behaviour in response to acute stressors, and helps regulate key life history decisions such as reproduction. Evidence in the literature has demonstrated that exposure to contaminants impacts the stress response and associated behaviours, however, these are few in number. Triphenyl phosphate (TPHP) is an organophosphate flame retardant that has been classified as a priority chemical under the Government of Canada’s Chemicals Management Plan. Preliminary studies have demonstrated that TPHP causes behavioural changes, physical deformities and changes to the gene expression of the stress axis (Hypothalamus-pituitary-interrenal (HPI) axis) in zebrafish (Danio rerio). However, little is known about this compound’s potentially toxic effects in other taxa. The objective of my thesis is to determine the effects of TPHP on stress and stress-related behaviour in Japanese Quail. Developing quail were exposed to TPHP in ovo and orally for the first week of life. Treatment groups consisted of safflower oil (control), predicted environmentally relevant levels of TPHP (5 ng/g) and higher levels of TPHP (50 ng/g and 100 ng/g). In addition to measures of mortality and deformities, individuals from all treatment groups were subjected to behavioural tests involving tonic immobility, contact with a novel object and exploration of a novel environment. Baseline and stress-induced corticosterone concentration were also measured. Chicks exposed to higher doses of TPHP (100 ng/g) administered significantly more pecks (18.0 ± 2.8) upon a novel object in comparison to the lower dose group (5 ng/g) and control (10.3 ± 0.9 and 9.5 ± 1.4 pecks respectively). As mentioned above, while baseline and corticosterone concentrations were measured, the results were difficult to interpret due to the assay being difficult to validate, and only 44% of the birds were successfully blood sampled past the 3 minute mark. Baseline values varied between 0.42 ± 0.1 and 2.9 ± 0.95 ug/mL, while stress values varied between 2.3 ± 0.61 and 11 ± 1.9 ug/mL. The change from baseline to stress samples varied between 2.0 ± 0.4 and 7.65 ± 1.4 ug/mL. The average pre-stress corticosterone was lower than the post-stress corticosterone, however there was a positive relationship seen between sampling time and post-stress corticosterone concentrations. Lastly, no relationship between TPHP and corticosterone was observed, which should be interpreted with caution given the issues with the assay. Overall, these data suggest that TPHP affects neophobic behaviour in Japanese Quail exposed to 100 ng/g of TPHP. This exceeds the 5 ng/g that was initially defined as an environmentally relevant dose when the study was designed. However, in light of recent evidence that TPHP is rapidly metabolized in birds, this implies our initial definition of environmental relevance may not be correct. Alterations to the stress response could prove to be extremely detrimental to any species, as it could lower the ability to cope with acute environmental changes, and evade predators. Increasing our understanding of behavioural effects of TPHP in birds will support risk assessment to effectively minimize any potential deleterious impacts on wildlife

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