**1. Introduction**

Boron (B) is an essential element for living organisms. B has different physiological effects on living organisms at low concentrations, whereas it has toxic effects at higher concentrations. Generally, B is not found as an element in nature and is commonly found in the form of boric acid, borax, and other complex forms. People are affected by boron:


Since boron is ubiquitous, it will be accepted that no limit can be drawn for being under the influence of boron [1].

Animals and humans could be ingested higher levels of B through foods or may be exposed to boron due to occupational conditions as inhalation, dermal or oral exposure. During the exposure, damaged and injured absorption sites can lead to increased absorption. In some cases, dermal higher exposures to B could result in death. Boric acid could be fatal after higher ingestion [2, 3]. More studies are needed about the cellular toxicity mechanisms of B and B compounds at tissue level. Higher B exposure could cause:


As a normal consequence of boron uptake from food and drinking water, human tissues and body fluids contain B. Boron found in soft tissues is close to the blood level. B can accumulate in bones. Muscle tissue, heart, lung, and intestine contain lesser amounts of boron [6, 7]. The World Health Organization compared the blood levels of ingesting boron through drinking water and diet in humans and rats. The distribution of boron in blood and tissue samples for human and rat species, boron kinetics may be the same for both species [8].


#### **Table 1.**

*Boron compounds and toxic effects.*

Numerous studies on humans and laboratory animals have revealed that more than 90% of borates taken into the organism are removed from the organism in the form of boric acid. It has been reported that boric acid can form complexes with different biological molecules depending on the dose [9].

Regardless of the route of its uptake into the organism, the elimination of boron mainly occurs by glomerular filtration. Glomerular filtration is 3–4 times faster in rats than in humans, and it has been reported that more than 90% of boron, which is taken into the organism by various ways in humans, is removed through urine within the first 24 hours [10, 11].

The data obtained from animal studies are not enough for determining the Bor's potential of causing cancer to human [12]. Boron was not evaluated as a carcinogen by EPA (US Environmental Protection Agency) and NTP (US National Toxicology Program), IARC (International Agency for Research on Cancer) [8]. The studies about boron and its compounds mainly focus on their toxicologies. In the studies about boron exposure, data are stated as equivalent of boron for providing compared data. Under the physiological pH conditions, borate salts are completely converted to boric acid; based on this, it was stated that boric acid and borate salts have similar toxicological properties [13].

In this chapter, we aimed to review current toxicity data of B, and B compounds.
