Subchronic toxicity study of ozonated and ozonated/chlorinated humic acids in Sprague-Dawley rats: a model system for drinking water disinfection

Abstract

Male and female Sprague-Dawley rats were administered drinking water containing humic acids either nondisinfected or following ozonation (03) or ozonation/ chlorination (03/Cl2) for 90 consecutive days. Test animals drank either of two concentrations of humic acids, 0.25 and 1.0 g/L total organic carbon (TOC), while controls received phosphate-buffered, distilled water. No consistent significant treatment-related effects were observed in body weight gain, organ weights, food or water consumption, or hematological and clinical chemistry parameters. No target organs were identified from the histopathological examination of the tissues. The most significant observation, an increase in liver to body weight ratio for the male animals in the 1.0 g/L 03/Cl2 humic acid group, was not observed in any other group, nor was it corroborated via any biochemical measurements or histopathological analysis. Kidney lesions, primarily chronic progressive nephropathy, were a common observation in both controls and treated groups with no apparent relationship to either humic acid concentration or the disinfection process.

Ozonation of humic acid in water

“…3,4 Moreover, HAs are precursors of disinfection byproducts (DBPs) such as halogen-organics that are formed after water chlorination, which presents a major problem in drinking water treatment. 5,6 Removal of HAs has long been of concern in water treatment due to their diverse reactivity and abundance in natural waters. Ozone, as a powerful oxidizing reagent, could react with the organic matter present in water through different mechanisms involving direct molecular reactions and hydroxyl radical (OH . )…”

A toxicological evaluation of a fulvic and humic acids preparation

“…While our 90-day study was not suggestive of any thyrotoxicity of the test item, in the study by Daniel et al thyroid lesions that could be indicative of the presence of a goitrogen in their test item or iodine sequestration by HA in the gastrointestinal track were observed [ 31 ]. Because some known goitrogenic substances have been reported as degradation products of humic substances [ 68 ], further investigations into the toxicological potential of blk.…”

“…We investigated the repeated-dose toxicity of our test item in rats and observed several statistically significant alterations in various parameters that were of low magnitude and considered to be without toxicological concern. Interestingly, with respect to effects of humic substances on the thyroid, Daniel et al observed an increased incidence in histological thyroid lesions (colloid depletion, minimal severity and follicular cysts) in male Sprague-Dawley (SD) rats administered a single dose of a commercial HA preparation (Fluka, Switzerland) as a control substance in a subchronic toxicity study of the same HA subjected to ozonation (O 3 -HA) or subjected to both ozonation and chlorination (O 3 /Cl 2 -HA); however, thyroid hormone levels were not measured in the study [ 31 ]. Thyroid colloid depletion was also observed in high-dose O 3 /Cl 2 -HA group males at lower incidence while thyroid lesions were not observed in the buffered water control or O 3 -HA high-dose groups.…”

“…However, some studies have shown positive or equivocal results in both mutagenicity as well as general toxicity tests [ 22 , [29] , [30] , [31] , [32] ]. Additionally, the European Food Safety Authority (EFSA) evaluated an unpublished subchronic toxicity study in rats of a mixture of humic and fulvic acids with added minerals and determined a no observed adverse effect level (NOAEL) of 50 mg/kg bw/day due to body and organ weight decreases at higher doses that could not be laid to rest due to the absence of histological evaluations [ 21 ].…”

Kinetic Study of Humic Acid Ozonation in Aqueous Media

“…Due to the fact that they contain both aromatic and aliphatic components with primarily carboxylic and phenolic functional groups, HAs are very resistant to biodegradation and contribute to the brownish-yellow color of water [1,2]. Most significantly, HAs are precursors of disinfection by-products (DBPs) such as halogen-organics that are formed after water chlorination, which causes a major problem in drinking water treatment [3]. Several oxidation techniques for the treatment of HAs from water have been introduced, e. g., photocatalytic oxidation [4,5], ozonation [6 -8], and the coupled system of photo-catalysis and ozonation [9].…”