Power laws describing the dependence of metabolic rate on body mass have been established for many taxa, but not for prokaryotes, despite the ecological dominance of the smallest living beings. Our analysis of 80 prokaryote species with cell volumes ranging more than 1 000 000-fold revealed no significant relationship between mass-specific metabolic rate q and cell mass. By absolute values, mean endogenous mass-specific metabolic rates of non-growing bacteria are similar to basal rates of eukaryote unicells, terrestrial arthropods and mammals. Maximum mass-specific metabolic rates displayed by growing bacteria are close to the record tissue-specific metabolic rates of insects, amphibia, birds and mammals. Minimum mass-specific metabolic rates of prokaryotes coincide with those of larger organisms in various energy-saving regimes: sit-and-wait strategists in arthropods, poikilotherms surviving anoxia, hibernating mammals. These observations suggest a size-independent value around which the mass-specific metabolic rates vary bounded by universal upper and lower limits in all body size intervals
Mining in the State of Minas Gerais-Brazil is one of the activities with the strongest impact on the environment, in spite of its economical importance. Amongst mining activities, acid drainage poses a serious environmental problem due to its widespread practice in gold-extracting areas. It originates from metal-sulfide oxidation, which causes water acidification, increasing the risk of toxic element mobilization and water resource pollution. This research aimed to evaluate the acid drainage problem in Minas Gerais State. The study began with a bibliographic survey at FEAM (Environment Foundation of Minas Gerais State) to identify mining sites where sulfides occur. Substrate samples were collected from these sites to determine AP (acidity potential) and NP (neutralization potential). The AP was evaluated by the procedure of the total sulfide content and by oxygen peroxide oxidation, followed by acidity titration. The NP was evaluated by the calcium carbonate equivalent. Petrographic thin sections were also mounted and described with a special view to sulfides and carbonates. Based on the chemical analysis, the acid-base accounting (ABA) was determined by the difference of AP and NP, and the acid drainage potential obtained by the ABA value and the total volume of material at each site. Results allowed the identification of substrates with potential to generate acid drainage in Minas Gerais state. Altogether these activities represent a potential to produce between 3.1 to 10.4 billions of m³ of water at pH 2 or 31.4 to 103.7 billions of m³ of water at pH 3. This, in turn, would imply in costs of US7.8to25.9millionstoneutralizetheaciditywithcommerciallimestone.Thesefiguresareprobablyunderestimatedbecausesomemineswerenotsurveyed,whereas,inothercases,surfacesamplesmaynotrepresentreality.Amorereliablestate−wideevaluationoftheaciddrainagepotentialwouldrequirefurtherstudies,includingalargernumberofsamples.Suchinvestigationsshouldconsiderotherminingoperationsbeyondthescopeofthisstudyaswellasthekineticsoftheacidgenerationbysimulatedweatheringprocedures.<br>Adespeitodaimporta^nciaecono^micadeatividadesmineraloˊgicasparaoestadodeMinasGerais,perceber−sequeelascausamsignificativoimpactoaoambiente.Drenagemaˊcidaeˊumdosaspectosambientaisconsideradospelaatividadeemfunc\ca~odeseusimpactos.Elatemorigemapartirdaoxidac\ca~odesulfetosmetaˊlicosqueacidificamasaˊguas,compossibilidadedemobilizarelementostoˊxicosepoluirosrecursoshıˊdricos.Estetrabalhotevecomoobjetivorealizarumaavaliac\ca~opreliminardoproblemaemMinasGerais.OtrabalhoteveinıˊcioapartirdeumlevantamentobibliograˊficojuntoaFundac\ca~oEstadualdeMeioAmbiente(FEAM)paraidentificarminerac\co~escujomineˊrioestaˊassociadoasulfetos.Amostrasdossubstratosforamretiradasparadeterminaropotencialdeacidez(AP)edeneutralizac\ca~o(NP).APfoiavaliadopordoisprocedimentos:peloteortotaldesulfetosepelaoxidac\ca~ocomperoˊxidoseguidadatitulac\ca~oaˊcida.ONPfoiavaliadopeloteorequivalentedecarbonatodecaˊlcio.La^minaspetrograˊficasforampreparadasparaadescric\ca~omineraloˊgicacome^nfaseemsulfetosecarbonatos.Obalanc\coaˊcido−base(ABA)foideterminadopeladiferenc\caentreAPeNP,enquantoopotencialdegerac\ca~odeaˊguasaˊcidasfoiobtidopelovalordeABAeovolumetotaldematerialdecadaatividademineraˊria.OsresultadospermitiramidentificarquatrosubstratoscompotencialparagerardrenagemaˊcidanoestadodeMinasGerais.Juntas,estesmateriaisrepresentamumpotencialdegerac\ca~odecerca3,14a10,37bilho~esdemetroscuˊbicosdeaˊguaapH2,0ou31,4a103,7bilho~esdemetroscuˊbicosdeaˊguaapH3,0.EstesvaloressignificamcustosentreUS 7,8 e 25,9 milhões para neutralizar a acidez com o uso de calcário. Estas estimativas são provavelmente subavaliadas, uma vez que algumas minerações não foram incluídas no levantamento e, para outras, as amostras superficiais podem não representar a realidade. Uma avaliação mais rígida do potencial de drenagem ácida em nível estadual requer estudos futuros. Estes estudos precisariam incluir um número maior de amostras e mineradoras não incluídas neste trabalho. Eles poderiam considerar, ainda, a cinética de geração de acidez por meio de procedimentos de intemperismo simulado