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Boron is the fifth element of the periodic table and the only electron‐deficient nonmetallic element. Consequently, boron has a high affinity for electronegative atoms such as oxygen and forms strong covalent boron–oxygen bonds in compounds known as borates . Boron is an essential micronutrient in plants and nutritionally important in animals and humans. Boron occurs naturally in all foods; fruits, vegetables, and nuts contain the highest levels. The toxic effects and pharmacokinetics of boron and borates are reviewed. The inorganic boron‐containing materials share many chemical and biological characteristics thought to be due to unique properties of the boron element. This chapter reviews the shared characteristics and the individual inorganic boron‐containing compounds that have a significant use in industry. Some of the more important physical and chemical properties of boron compounds of commercial significance and widespread exposure are listed.

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: A variety of regulatory requirements for ecotoxicity test data exist in the US and each of these is able to specify what test protocols and endpoints are used. General practice is to calculate regression curve endpoints, usually EC50 values, for acute tests, and hypothesis test endpoints (e.g. NOEC, LOEC) for chronic studies. However, tests of wastewater effluents often use a hypothesis test endpoint which has been derived using site-specific information to represent a pass-fail standard for compliance. Field work, such as site assessments, tends to use hypothesis tests, but such work does not seek the doseresponse curve sought in standard laboratory tests. The risk-based approaches being developed use cither type of endpoint, but this seems to be an accommodation to existing data; preference is for dose-response curves, not just a single ECx value. Endpoints are only one component of the conventional paradigm of environmental protection. Experience with various tests and endpoints suggest several perspectives: quality is critical, test species must be reliable and relevant, extrapolations will dominate decisions, and basing environmental decisions on the most sensitive endpoint of the most sensitive species may not remain a feasible paradigm for protecting ecological systems.

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