*Flame Retardants: New and Old Environmental Contaminants DOI: http://dx.doi.org/10.5772/intechopen.104886*

environment [78]. Another issue is that their concentration in the product decreases over time, thereby reducing its FR properties [6].

To understand the chronic consequences related to the use, adverse effects on the environment, and toxicity of these FRs, their underlying mechanisms must be understood. Moreover, understanding the properties of these FRs and how they behave upon contact with living organisms and the ecosystem is crucial. Organic organophosphate FRs are considered emerging pollutants, and they have been widely studied in recent years.

#### **3.1 Physicochemical characteristics**

In general, organophosphates have different physicochemical characteristics. These organic compounds usually have reasonable solubility in water, but this varies according to molecular weight.

Organophosphates with low molecular weight are easily found in the aquatic environment, while compounds with high molecular weight are found in general nature. The octanol/water partition coefficient (log *K*ow) of organophosphates ranges from 9.8 to 10.6, which means that they are more lipophilic than hydrophilic. However, they have better solubility in water than BFRs [6, 80].

Organophosphate distribution in the air and the environment varies. According to Henrys law, the vapor pressure also varies [6]. Variations in physicochemical characteristics are directly related to variations in biological effects. Thus, clarifying the mechanisms of these compounds is important [81].

BPA-DP is an organic additive FR with boiling point of 680°C and melting point ranging from 41 to 90°C, low solubility in water ( 0.4 mg/l), and log *K*ow of 4.5. RDP is found in commercial blends with BPA-DP and is also an additive FR. It has a boiling point of 587°C, no melting point, and is even more insoluble in water (1.11 <sup>10</sup><sup>4</sup> mg/l), with a log *<sup>K</sup>*ow of 7.41. Both compounds are widely used together due to their advantageous characteristics, such as good thermal stability, high efficiency, and low volatility. They are primarily used as flat-screen protection for TVs and other electronics such as monitors and smartphones [6, 82].

Diethylphosphinic acid, on the other hand, has good solubility in water (4.52 104 mg/l), log *<sup>K</sup>*ow of 0.68, melting point of 14°C, and lower boiling point (320°C). DCP also has a low boiling point (235°C), melting point of 38°C, but lower solubility in water (0.24 mg/l) and log *K*ow of 4.51. Diethylphosphinic acid is an important compound because it is also a product of the thermal decomposition of aluminum diethyl phosphinate (AlPi), another FR that has been gaining visibility [6, 83].

Melamine polyphosphate is a nitrogen-containing FR. It is chemically linked to the polymer molecule, so it is not considered an additive FR [84]. This compound has the boiling point of 558°C, the melting point above 400°C, good solubility in water (around 1 g/l), and log *K*ow of 2.3 [6].

TCP is an additive FR. It is an ester of cresols and phosphoric acid, with the boiling point of 439°C, melting point of 77°C, low solubility in water (0.36 mg/l), and log *K*ow of 5.11. It is widely used in lubricants, hydraulic fluids, and engine oil. All its isomers (*ortho*-cresol, *para*-cresol, and *meta*-cresol) are active, but *o-*TCP has gained attention because it is related to cases of neuropathy induced by organophosphates [6, 85].

TPhP is one of the most commonly used additive organophosphates in the industry, and it is also the main contaminant in nature. Its boiling point is 370°C, its melting point is 49°C, it is sparingly soluble in water (1.9 mg/l), and its log *K*ow is 4.59. Because TPhP has hydrophobic properties, it has a great affinity for sediments and

soil, which is why it is frequently found in aquatic environments [6, 86]. Organophosphate distribution in air depends mainly on the values of the octanol-air coefficient (log *K*oa). Compounds with log *K*oa less than 10 are easily found in the gas phase, while higher values are necessary for compounds to be detected in the particulate form and associated with dust. Values for all the compounds are not yet clear. However, TPhP, for example, has a log *K*oa of 10.5 and is easily found in many forms in the home environment [87, 88].

ALPi has excellent heat stability, producing less smoke during burning. The ALPi log *K*ow is 0.44 and the water solubility is around 1 mg/l, suggesting low hydrophilic properties. Thus, soil and sediments can be the main target of the accumulation of this compound [89].

Organophosphates have relevant physicochemical characteristics for their applications. In general, they are interesting FRs because they decompose at a lower temperature than polymers used in the production of materials. Thus, heating compounds with phosphorus triggers phosphoric acid formation. This acid envelopes the material, protecting it from pyrolysis and preventing toxic gases from being formed [6, 90].

**Table 4** summarizes the chemical structure and physicochemical properties of organic organophosphates.

### **3.2 Environmental occurrence and ecotoxicological effects**

Although organic organophosphates have more interesting characteristics and offer more benefits than BFRs, they are often found in the environment (indoor dust, air, water, soil, and sediments) [91–93].

Because organophosphate particles are just additives and do not fully bind to the material they are incorporated into, they are easily dispersed. This causes them to be absorbed by suspended dust. Thus, indoor dust is an interesting indicator of indoor exposure to industrial chemicals [64].

Huang et al. [81] analyzed indoor dust from Australian homes, to find that TPhP is one of the most common compounds therein. This is expected if we consider the recurrent use of TPhP. The authors also found BPA-DP in abundance. In fact, this compound is used as a substitute for DecaBDE. The authors concluded that many organophosphates are present in the samples, presenting a high risk to human health [81].

Despite being mostly lipo-soluble, some organic organophosphates have good solubility in water. This has led to their detection in drinking water because treatment stations cannot eliminate these compounds effectively. Thus, the occurrence of organic organophosphates in the aquatic environment poses as much risk to human beings as to the aquatic ecosystem [94].

To identify the presence of organophosphates in water, Kim and Kannan [95] analyzed several samples, such as river water, rainwater, sea water, and tap water samples, collected from various locations in New York State. All the samples presented numerous organophosphates. Chlorinated compounds were identified as the most abundant due to their greater hydrophilicity. Among organic compounds, TPhP was found in over 90% of the river water samples.

On the other hand, compounds with greater lipophilicity are easily found in sediments and aquatic organisms, being the cause of bioaccumulation. In sediments, the composition is directly related to adsorption capacity. For example, clay-rich areas favor greater adsorption of these FRs [96].
