Lead in freshwaters

Standards for lead in freshwaters are based upon both the protection of aquatic life and the quality of the water for public supply. The standards for public water supply have already been discussed (Section 6.2.1). 

In England, the Anglian Water Authority has adopted maximum desirable and maximum permissible lead concentrations of 0.4 and 0.5 mg dmT respectively as criteria to protect rivers used for fishing (trout, dace, roach, perch, bream) [7 ]. 

The toxicity of a metal to aquatic life is closely related to the chemical form of the metal, although as yet the precise relationship between chemical form and toxicity is not clearly established. The chemical form depends in turn on other water quality parameters (Section 3.4) and is thus likely to be highly variable. 

This mitigates against the simplistic application of a single standard to protect aquatic life in all waters. At the same time, it complicates the derivation, application and adminstration of standards individually designed to suit a particular water. 

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The Co-APDC co-precipitation procedure for preconcentration has been shown to be suitable for the determination of lead in freshwater samples. Cadmium determination at concentrations ca. 0.1 mg l-1 in freshwater can also be performed using this procedure at lower concentrations an... 

May, T.W. and G.L. McKinney. 1981. Cadmium, lead, mercury, arsenic, and selenium concentrations in freshwater fish, 1976-77 — National Pesticide Monitoring Program. Pestic. Monit. Jour. 15 14-38. 

Everard, M. and P. Denny. 1984. The transfer of lead by freshwater snails in Ullswater, Cumbria. Environ. Pollut. 35A 299-314. 

Fraser, J. 1980. Acclimation to lead in the freshwater isopod Asellus aquaticus. Oecologia 45 419-420. Friberg, L. 1988. The GESAMP evaluation of potentially harmful substances in fish and other seafood with special reference to carcinogenic substances. Aquat. Toxicol. 11 379-393. 

May, T.W. and G.L. McKinney. 1981. Cadmium, lead, mercury, arsenic, and selenium concentrations in freshwater fish, 1976-77 — National Pesticide Monitoring Program. Pestic. Monitor. Jour. 15 14-38. McDonald, L.J. 1986. Suspected lead poisoning in an Amazon parrot. Canad. Vet. Jour. 27 131-134. McLean, R.O. and A.K. Jones. 1975. Studies of tolerance to heavy metals in the flora of the rivers Ystwyth and Clarach, Wales. Freshwater Biol. 5 431 -444. 

Ruparelia, S.G., Y, Verma, N.S. Mehta, and S.R. Salyed. 1989. Lead-induced biochemical changes in freshwater fish Oreochromis mossambicus. Bull. Environ. Contam. Toxicol. 43 310-314. 

In studies of the concentrations of arsenic, bromine, chromium, copper, mercury, lead and zinc in south-eastern Lake Michigan, it was shown that these elements concentrated near the sediment water interface of the fine-grained sediments. The concentration of these elements was related to the amount of organic carbon present in the sediments (161). However, it was not possible to correlate the concentration of boron, berylium, copper, lanthanum, nickel, scandium and vanadium with organic carbon levels. The difficulty in predicting the behaviour of cations in freshwater is exemplified in this study for there is no apparent reason immediately obvious why chromium and copper on the one hand and cobalt and nickel on the other exhibit such variations. However, it must be presumed that lanthanium might typify the behaviour of the trivalent actinides and tetravalent plutonium. 

Pyrite is formed by two mechanisms in freshwater sediments. Fram-boidal pyrite results from reaction of iron monosulfides with S° (15), a slow reaction leading to gradual conversion of iron monosulfides to pyrite. In contrast, single crystals of pyrite are formed rapidly through reaction of Fe2+ and poly sulfides (161). Framboidal pyrite has been reported in lake sediments (37, 189), where it appears to form in microenvironments of plant or animal skeletons (cf. 35, 36). Rapid formation of pyrite has been observed in short-term measurements of sulfate reduction with SO/-. Up to 90% of reduced has been observed in pyrite after incubations of 1-24 h (72, 79, 98). A large fraction of inorganic S in the form of pyrite in surface sediments also has been interpreted to indicate rapid formation (112, 190). As discussed later, there is little evidence for extensive conversion of monosulfides to pyrite. 

It is not yet clear which estimates of the ratio between the levels of protein and of carbohydrate metabolism during hypoxia should be regarded as reliable. It seems likely that the increase in respiratory quotient in freshwater fish to values of 2.5-2.8, as found by Mohamed and Kutty (1983a, 1986), indicates a predominance of protein expenditure over that of carbohydrate. A hypoxic environment shifts the acid-base balance of the fish towards acidosis (Kotsar, 1976), thereby inducing the redistribution of electrolytes, alteration of ion exchange and the activity of Na+-K+-Mg2+-ATPases and alkaline phosphatases. It also leads to an increased level of C02 in the blood, which enhances the bicarbonate buffer system (Kotsar, 1976). In section 2.1, we... 

Lam, M.T., Chakrabarti, C.L., Cheng, J. and Pavski, V. (1997) Rotating disk electrode voltammetry/anodic stripping voltammetry for chemical speciation of lead and cadmium in freshwaters containing dissolved organic matter. Electroanalysis, 9, 1018-1029. 

Environmental quality standards (EQSs) are widely used to help protect the environment and human health and are considered by many to consist simply of the stated limit value for a substance plus, perhaps, the time over which the standard applies. An example of this might be an annual average EQS for lead in water of 7.2 pg Ir1 to protect the freshwater environment as proposed in the Water Framework Daughter Directive on EQS (European Commission [EC] 2006). 

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