Toxic concentrations of heavy

Table 16.13 Toxic concentrations of heavy metals to rainbow trout...

This ongoing removal of S042" shows that SRB metabolism continues despite reports of toxic concentrations of heavy metals (Poulson etal. 1997). 

Table I. Reported Values of Toxic Concentrations of Heavy Metals in Anaerobic Waste Treatment...

Hooser SB Purdue University, West Lafayette, IN Feed additives and tissue concentrations of heavy metals and/or alterations in toxicity U. S. Department of Agriculture... 

On a worldwide basis, toxic concentrations of the heavy metals have thus far been limited to industrialized harbors. The only metals that appear to have accumulated to toxic levels on a regional scale are mercury, cadmium, and lead in the Arctic Ocean. This concentration of mercury and lead has been fecilitated by a natural process, called the grasshopper effect, which acts to transport volatile compoimds poleward. This transport plays a major role in redistributing the volatile organic pollutants, such as the PCBs, and, hence, is discussed at further length in Chapter 26.7. The process responsible for the cadmium enrichment in the Arctic appears to involve low-altitude transport of the fine particles that compose Arctic haze. 

The initial species present, their relative concentrations, the induction of their enzymes, and their ability to acclimate once exposed to a chemical are likely to vary considerably, depending upon such environmental parameters as temperature, salinity, pH, oxygen concentration (aerobic or anaerobic), redox potential, concentration and nature of various substrates and nutrients, concentration of heavy metals (toxicity), and effects (synergistic and antagonistic) of associated microflora (Howard and Banerjee, 1984). Many of the parameters affect the biodegradation of chemicals in the environment as well as in biodegradation test systems used to simulate the environment. 

Heavy metals, like lead and mercury, have been recognized as toxic poisons for centuries. Further, toxic concentrations of mercury, for example, can trigger several effects like autoimmune diseases, infections, unexplained chronic fatigue, depression, nerve impairment, memory problems, decreased mental clarity, and bowel disorders. For several decades, mercury vapor exposure has caused severe health problems among chloralkali workers. This is only an example. It may be repeated that education can effectively minimize exposure to hazardous metals. Basic information and training for proper handling of toxic chemicals will reduce potential adverse health effects. 

Drilling fluid additives Many of the additives used in the past for drilling fluids have contained potential contaminants of concern, such as chromium in lignosulfonates. Also, barite weighting agents may contain concentrations of heavy metals such as cadmium or mercury. The use of such additives has diminished. However, it is important to select additives that are less toxic and... 

Before a brine is disposed of onto a soil or into a water system, an evaluation should be carried out to determine the brine s potential to contaminate such systems. In carrying out such an evaluation, one must first determine the concentrations of heavy metals and toxic organics in the brine. Since the mechanism of detoxification is basically dilution of NaCl, certain procedures for brine disposition should be followed, depending on the content of heavy metals and boron. When the brine contains high concentrations of heavy metals and boron, the first consideration must be the potential of dilution to bring the concentration of heavy metals and boron to within an acceptable range. The next concern is to be sure that the magnitude of EC and SAR upon dilution will be within the critical thresholds (<2 and <5, respectively). 

The impact of the various substances listed above may result in low-quality water with bad taste, odor, and turbidity or toxicity from the high concentration of heavy metals, chlorinated hydrocarbons, and/or pathogenic bacteria and viruses. Water purity, however, is not a prerequisite to good water quality with respect to human consumption or agricultural and industrial uses. When water contacts soil, the latter contributes dissolved minerals (e.g., Ca, Mg, K) which may increase the potential water quality for biological uses because these minerals serve as nutrients. 

By means of plants (used as food) and water, the soil pollutants threaten human and animal organisms and disturb natural cycles. Concentrations of heavy metals (Hg, Cu, Cd, Pb) and also other toxic metals, such as Zn, Se and As in soils are continually increasing by the action of intense human activity (civilization, industrialization, road transport). Frequently used pesticides and industrial fertilizers also make considerable contributions to the soil pollution. 

The problem of the speciation of metals in sediments continues to attract attention, both from the point of measurement techniques and from the point of bioavailabihty and, consequently, effects such as toxicity. Some workers prefer to measure total metals after full digestion of sediments with hydrofluoric acid, others favor sequential extractions [84]. The concentrations of heavy metals in coastal sediments are remarkably similar world-wide [85] Cu30pg/g, Ni 30 )ig/g, Pb 40 )ig/g, Zn 120 pg/g, Ag 1 pg/g, Cd 1 pg/g, Hg 0.5 pg/g dry sediment containing at least 20% of silt and clay, respectively. High levels are about... 

All tobacco products, including snuff, contain toxic heavy metals and many carcinogenic substances. The concentrations of heavy metals in Indian snuff samples is significantly much less compared to those in snuff samples from South Africa and U.S.A. ... 

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