# Chemicals from Brominated Flame Retardants: Analytical Methods, Occurrence, Transport and Risks
## 4 Transport Mechanisms of BFRs  
Understanding the transport mechanisms of BFRs and associated chemicals is crucial for assessing their environmental fate and potential risks. BFRs are released into the environment in three main ways: (1) as volatile substances are released directly into the environment, (2) as products containing these chemicals break down and release the chemicals into the environment, and (3) as products come into direct contact with environmental media (Figure 2). Moreover, BFRs can interact with other emerging contaminants such as heavy metals and micro(nano)plastics (M/NPs), complicating their environmental behavior and impact [84]. The co-occurrence of BFRs and heavy metals can lead to complex chemical interactions that influence their mobility, bioavailability, and toxicity. Heavy metals can bind to BFRs, potentially altering their transport dynamics and enhancing their persistence in the environment. Studies have shown that the presence of heavy metals can affect the sorption and desorption processes of BFRs in soil and aquatic systems, modifying their environmental fate [85]. The hydrophobic nature of both BFRs and M/NPs enables BFRs to adsorb onto plastic particles, which can then be transported over long distances by water currents and wind [86]. This interaction can increase the potential for the bioaccumulation and biomagnification of BFRs in aquatic organisms, as M/NPs are readily ingested by marine life. Additionally, the degradation of M/NPs can release adsorbed BFRs back into the environment, further complicating their ecological impact [86].  
Figure 2: Migration pathways of BFRs in the environment (modified from [PERSON] et al. [87]).  
BFRs may evaporatively or by fugitive migration reach the atmosphere during manufacturing and usage. In a similar vein, these substances may evaporate from garbage during disposal. BFRs discharged into the atmosphere can readily interact with particles and sink into the aquatic environment because of their octanol-water partition coefficient (log K\({}_{\text{ow}}\)). The amount of BFRs in water can be greatly impacted by runoff from polluted soils. For instance, [PERSON] et al. [87] discovered that in the coastal East China Sea, surface runoff was responsible for 15.1% of the PBDE contamination. [PERSON] and [PERSON] [88] found that summertime concentrations of PBDEs were considerably greater in Wuhan than wintertime concentrations. They hypothesized that this difference may be attributed to summertime rainfall runoff.  
This section discusses the transport mechanisms of BFRs in the atmosphere, surface water, and soil, focusing on their dispersion, deposition, sorption, mobility, and contaminant transfer pathways [89]. These factors are also responsible for the movement of BFRs. Transport is a movement caused by ambient wind flow and direction. Dispersion results from local turbulence/disturbance, while deposition is the downward movement of pollutants to the ground surface, which relies on precipitation, scavenging, and sedimentation [90]. However, studies covering the transport mechanisms of BFRs are still scarce.