Quantification and Prediction of the Detoxifying Properties of Humic Substances Related to Their Chemical Binding to Polycyclic Aromatic Hydrocarbons

Abstract

Effects of 27 different humic materials on the toxicity of polycyclic aromatic hydrocarbons (PAH) were studied for crustacean Daphnia magna. Sources included isolated humic acids, fulvic acids, and their combination from soil, peat, and freshwater. The PAH used were pyrene, fluoranthene, and anthracene. The observed reduction in toxicity of PAH in the presence of humic substances (HS) was shown to be a result of the detoxification effect caused by the chemical binding of PAH to HS and of the direct effect of HS on D. magna. An approach was developed to quantify the detoxifying impact of humic materials related to their chemical binding to PAH with a use of the "constant of detoxification" or "toxicological partition coefficient" K(oc)D. The latter was proposed to determine by fitting the experimental relationships of the detoxification effect versus concentration of HS. The obtained K(oc)D values were well tracked by the corresponding partition coefficients determined by the fluorescence quenching technique (K(oc)fq): K(oc)D=b x K(oc)fq, b (mean+/-Cl, n=26, P=95%)=2.6+/-0.3, 4.6+/-0.6, and 6.0+/-1.4 for pyrene, fluoranthene, and anthracene, respectively. The predictive relationships between the structure and detoxifying properties of humic materials in relation to PAH were developed. It was shown that the magnitude of the K(oc)D values correlated closely with the aromaticity of humic materials characterized with the 13C NMR descriptors (sigma(C)Ar, sigma(C)Ar/sigma(C)Alk) and atomic H/C ratio. The obtained relationships showed the highest detoxifying potential of the humic materials enriched with aromatics and allowed a conclusion on the chemical binding as the governing mechanism of the mitigating action of HS on the toxicity of PAH.

Effect of humic substances on toxicity of inorganic oxidizer bioluminescent monitoring

“…They are ubiquitous and result from the natural transformation of organic matter in soil and sediments. Among the effects of HS in the environment, increasing evidence indicates that they can act as natural attenuators of toxicity of heavy metals, surfactants, hydrocarbons, and organic oxidizers [2][3][4][5][6]. Elucidation of the detoxification mechanism by HS is of great interest [3,[7][8][9][10][11][12].…”

A study of the interaction between humic acids and acidic metabolites of phenanthrene by capillary electrophoresis

“…Their chemical structure has not yet been defined precisely, but, in any case, the HA molecules contain a great number of aromatic rings, aliphatic chains and functional groups (carboxylic, phenolic, hydroxylic, carbonylic, amine and amides). Consequently, they are able to interact with a wide range of pollulants and can influence the solubility, transport, bioavailability and lower the toxicity of water solutions of dangerous organic compounds, such as polycyclic aromatic hydrocarbons (PAH), for aquatic organisms [3].…”

“…Radiochemical studies on PAH biodegradation in the presence of HA have demonstrated the biogenic formation of chemically bonded compounds [5]. Chemical degradation techniques made evident the presence of reaction products (mainly esters) formed between PAH acidic metabolites and HA [3,4]. Besides, it was observed that a fraction of the acidic PAH was not chemically bonded but formed inclusion compounds [6].…”

Application of Chemically Accelerated Biotreatment to Reduce Riskin Oil-Impacted Soils

“…From the standpoint of bioavailability, interaction between dissolved organic matter (e.g. fulvic acids) and PAH has been reported to decrease PAH uptake and bioconcentration by, and/or toxicity to, higher organisms, for example Daphnia magna (Akkanen and Kukkonen, 2001;Perminova et al, 2001) and other aquatic organisms (Haitzer et al, 1999 & references therein). This, however, is in direct contrast to a spate of studies which have recently reported that addition of humic substances significantly stimulates microbial degradation of both polychlorinated biphenyls (Fava and Piccolo, 2002) and PAH (Haderlein et al, 2001;.…”