Hard water, toxicity

Penttinen, S., A. Kostamo, and J.V.K. Kukkonen. 1998. Combined effects of dissolved organic material and water hardness on toxicity of cadmium to Daphnia magna. Environ. Toxicol. Chem. 17 2498-2503. 

Solbe, J.F.D.L.G. and V.A. Flook. 1975. Studies on the toxicity of zinc sulphate and of cadmium sulphate to stone loach Noemacheilus barbatulus (L.) in hard water. Jour. Fish Biol. 7 631-637. 

Halter, M.T., W.J. Adams, and H.E. Johnson. 1980. Selenium toxicity to Daphnia magna, Hyallela azteca, and the fathead minnow in hard water. Bull. Environ. Contam. Toxicol. 24 102-107. 

Gensemer, R.W., Naddy, R.B., Stubblefield, W.A., Hockett, J.R., Santore, R. and Paquin, P. (2002) Evaluating the role of ion composition on the toxicity of copper to Ceriodaphnia dubia in very hard waters, Comparative Biochemistry and Physiology, Part C133 (1-2), 87-97. 

HMBC test is based on the U.S. EPA concept of Water Effect Ratio (WER), except that a bacterial response (MetPLATE) is used to determine metal bioavailability. Briefly, the methodology consists of spiking samples of both laboratory water (moderately hard water) and site water with a given metal and the mixtures are shaken for 60 min at 25°C. Afterwards, both mixtures are assayed for metal toxicity using MetPLATE. HMBC is determined as the ratio of IC50 of the metal in site water over IC50 of the metal in laboratory water. 

Water that contains substantial amounts of dissolved calcium and magnesium salts is called hard water. Water acquires these salts when it passes through soil and rocks that contain calcium and magnesium carbonates. While these salts are not toxic, they react with soaps and detergents to form an insoluble scum on sinks, bathtubs, and showers. When clothes are washed in hard water, some of the insoluble material adheres to the clothes and alters the way they feel. A device called a water softener can solve the hard-water problem by removing the excess calcium and magnesium ions. 

No water quality objectives or other water quality standards were found for the lanthanide metals. Aquatic toxicology data were only found for the lanthanide soluble salts. These soluble salts are known to have high chronic toxicity in fish, moderate chronic toxicity in green algae, and low acute toxicity in daphnids based on exposures in moderately hard water in terms of lanthanide per liter. 

The chemicals leached from these surfaces depend on the corrosive properties of the particular water as well as the chemical nature of the surface. Hard water tends to deposit a mineral layer on the inside of pipes and on other surfaces that essentially limits the access of water to the surfaces. On the other hand, soft water, particularly at lower pHs, can actively dissolve toxic metals such as lead or cadmium from pipes or solder. Copper in pipes is also frequently leached from pipes at high concentrations when the water has corrosive properties. Asbestos-cement has been used widely in water mains. The extraction of the asbestos fibers from these surfaces is also very much increased at lower pH and with soft water. The use of lead pipe and solder in household pipes has pretty much been abandoned in the United States. However, alloys of lead are still utilized in many faucets and brass fixtures (e.g., submersible pumps). Rather high concentrations of lead can result if water stands in these fixtures overnight. As a result it is always wise to avoid using the water first drawn from the tap in the morning for human consumption. Low levels of lead exposure in utero or in the first few years of life have been associated with delayed CNS development in humans and experimental animals. 

This test, along with the fish 96-h acute toxicity test, is one of the standbys in aquatic toxicology. Daphnia magna and D. pulex are the common test species. D. magna require a relatively hard water for its culture. They are large,... 

Sodium oleate (Na02C(CH2)isCH3), which is much less toxic in hard water, parenthesized value. 

Winner, R. W. (1985). Bioaccumulation and toxicity of copper as affected by interactions between humic acid and water hardness. Water Res. 19, 449-455. 

The former is of concern to domestic users of water, whereas the latter is a problem for engineers. On the other hand, soft waters have been linked with an increased incidence of cardiovascular disease. Other advantages of hard water include the neutralization of acid deposition and the reduction of the solubility of toxic metals (see Chapter 4 for more details). 

Hard water contains metallic ions, such as magnesium or calcium ions, that interact with soap to form insoluble films or scum. Hardness is not hazardous to health but may form scale in boilers and clog water pipes. Excess calcium and magnesium can be removed by ion exchange water softeners. SEE ALSO Green Chemistry Neurotoxins Toxicity Water Water Pollution. 

TOXICITY Marine waters should not exceed I/lOO of 96-hr LC50 (1.5 ppm) Fathead minnow Pimephales promelas) TLm 150 pg/L/96-hr, soft water more toxic in soft water than in hard water high acute and chronic toxicity to aquatic life... 

Inorganic ligands that complex metal ions can alter the effects that metal ions exert in natural waters. For example, the literature on fish toxicity contains references to the effects of water hardness on the toxicity of heavy metals. The general observation made is that heavy metals are much less toxic to fish in hard water than they are in soft water. We can provide an explanation of this result in terms of complex formation between the heavy metal copper and the alkalinity ions (HCOa" and COs "), since the alkalinity usually increases together with the water hardness. 

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