Firemaster 550 (FM550) is a flame retardant (FR) mixture which has become one of the most commonly used FRs in household items such as foam-based furniture and baby products. Because this mixture readily leaches from products, contamination of the environment and human tissues is widespread. Prior work by us and others has reported sex-specific behavioral deficits in rodents and zebrafish following early life exposure. In an effort to understand the mechanisms by which these behavioral effects occur, here we explored the effects of its constituents on behavioral outcomes previously shown to be altered by developmental FM550 exposure.  The FM550 commercial mixture is composed of two brominated compounds (BFR) and two organophosphate compounds (OPFRs) at almost equivalent proportions. Both the BFR and the OPFR components are differentially metabolized and structurally distinct, but similar to known neurotoxicants. Here we examined adult Wistar rat offspring socioemotional behaviors following perinatal exposure (oral, to the Dam) to vehicle, 2000 µg/day FM550, 1000 µg/day BFR or 1000 µg/day OPFR from gestation day 0 to weaning. Beginning on postnatal day 65 offspring from all groups were subjected to a series of behavioral tasks including open field, elevated plus maze, marble burying, social interaction tests, and running wheel.  Effects were exposure-, sex- and task-specific, with BFR exposure resulting in the most consistent behavioral deficits. Overall, exposed females showed more deficits compared to males across all dose groups and tasks. These findings help elucidate how different classes of flame retardants, independently and as a mixture, contribute to sex-specific behavioral effects of exposure.

Females were sacrificed on the day of estrus, and all rats were collected at approximately PND 247-261. Serum was collected from all rats via trunk blood. Wet weights were collected for adrenals, pituitaries, whole liver, kidneys, and hearts. The adrenals, pituitaries and median lobe of the livers was frozen on powdered dry ice and stored in -80°C. Using the ROUT outliers test (Q=1%), one BFR male and one OPFR female were identified and removed from adrenal and heart weight analysis, respectively. Final animal numbers were as follows: controls (14F, 14M); BFR (11F, 8M); OPFR (11F, 11M); and FM550 (14F, 15M).

Serum biochemistry was analyzed for 14 biochemical markers of general toxicity (listed in data set) to determine exposure effects. All procedures followed manufacturer’s protocols. On day of analysis, random samples of serum were thawed at 4°C and 120µL/sample added to the Comprehensive Diagnostic profile rotors (500–7123; Abaxis, Union City, CA). For quality assurance, a control sample (pooled from 20 random samples) was ran approximately every 25 samples. Rotors were placed in the VetScan VS2 Whole Blood chemistry analyzer and data exported. Final numbers were controls (13F,14M), BFR (11F,9M), OPFR (12F,11M) and FM550 (14F,15M). Although 21 statistical outliers from 6 biomarkers across female and male groups were identified, all data was used because no animal had greater than 2 outlying samples across all biomarkers.