IMPACT OF ARSENICALS ON NITRIFICATION 299 



aiid Epstein, 1970; Elespuru and Lijinsky, 1973; Eisenbrand, 

 Ungerer, and Preussmann, 1975). 



Generally organic arsenicals are reported to be between 10 and 

 100 times less toxic to biota than inorganic arsenicals (Versar, Inc., 

 1976). Our results showed this to be the case. Although arsenic in the 

 form of arsenate increased the lag phase of Nitrobacter at concentra- 

 tions as low as 0.1 and 1 mg/liter, cacodylic acid affected the 

 nitrifiers only at arsenic concentrations of 100 mg/liter and above. 

 Bollen, Norris, and Stowers (1977), studying forest floors and forest 

 soils treated with either cacodylic acid or MSMA, concluded that 

 these organic arsenicals should not have a significant adverse effect 

 on nitrogen metabolism of forest-floor and soil microorganisms. 



In aerobic systems, cacodylic acid is readily degraded to arsenate 

 (Woolson and Kearney, 1973). This fact, coupled with our observa- 

 tion of arsenate toxicity towards nitrifiers, points toward a potential 

 temporary buildup of nitrite in environments receiving high levels of 

 the nontoxic arsenical. 



In summary, our study showed (1) that these nitrification 

 systems provide reproducible results, (2) that Nitrobacter-type 

 organisms used in these systems are sensitive to arsenate, and (3) that 

 cacodylic acid is not directly toxic to nitrifiers. Field investigations 

 should be completed to test whether arsenicals inhibit Nitrobacter in 

 field situations. 



DISCLAIMER 



Mention of tradenames of commercial products does not 

 constitute endorsement or recommendation for use. 



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 Button, D. K., and S. S. Dunker, 1971, Biological Effects of Copper and Arsenic 



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 Campbell, N. E. R., and M. I. H. Aleem, 1965, The Effect of 2-Chloro, 



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vidth Pesticides. II. Formation, Chemical Properties and Carcinogenic 



