Humic Acid

Acute upper respiratory tract infections (AURTIs) are associated with a significant burden on society attributed to medical care and loss of productivity. Novel therapies that are able to shorten disease duration, while providing symptom relief and being well tolerated, are an unmet medical need. This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

Nanoparticles (NPs), heavy metal and natural organic matter (NOM) may simultaneously exist in the aquatic environment, where they will affect the behavior of each other and may enhance their toxicities. Studies on the influences of interactions between NOM and heavy metal ions on the behavior of NPs are scarce. In this study, combined effects of Pb2+ and HA on the aggregation behavior of TiO2 NPs in water environment were investigated by Dynamic light scattering (DLS) and Nanoparticle tracking analysis (NTA). The results illustrated that interactions between Pb2+ and HA could case the aggregation of TiO2 NPs obviously. The concurrence of Pb2+ and HA resulted in decreased critical coagulation concentration (CCC) and increased attachment efficiencies. Meanwhile, we found that the addition sequences of HA and heavy metal clearly influenced the aggregation kinetics of TiO2 NPs. At different addition sequences, the complex reaction between Pb2+ and HA changed the surface charge of TiO2 NPs, and caused the different aggregation behavior which depended on the complex locations and complex sites. Furthermore, the excitation-emission-matrix (EEM) fluorescence spectra was used to verify the significant effects of the complex interactions between Pb2+ and HA on the aggregation of TiO2 NPs. Our results would be significant for interpreting TiO2 behavior in the complicated water system. The complexation between Pb2+ and HA promoted the aggregation of TiO2 NPs, meanwhile, complex locations and complex sites played an important role.

Metal oxide nanoparticles (NPs) have been used increasingly and are likely to accumulate in natural water bodies, where they encounter and interact with other environmental chemicals. These interactions result in joint effects on biological systems and the environment. However, compared with the intensive research examining the toxicities of individual NPs, the toxicities of NP mixtures remain relatively unexplored. In this work, we studied the joint effects of NPs and their most likely coexisting chemicals in the environment, including NPs with different compositions, humic substances, and surfactants. Our results indicate that the joint effects of NP mixtures were usually simple addition, which is commonly adopted in real risk assessment. However, the joint effects obtained for mixtures that contained ZnO were exclusively associated with antagonism. In addition, the mixtures of NPs and surfactants resulted in complex joint effects, i.e., antagonistic, additive, and synergistic effects were found for the mixtures with ZnO, NiO, and Fe-oxide, respectively. Our study suggests that the assessments of the ecological risk of NPs, particularly ZnO NPs, should consider the impact of their coexisting chemicals in the environment.

The effect of non-functionalized and amino-functionalized multiwall carbon nanotube (CNT) exposure, as well as the impact of CNT presence on coexistent pesticide accumulation, was investigated in lettuce (Lactuca sativa L.). Lettuce seeds were sown directly into CNT-amended vermiculite (1000 mg L(-1)) to monitor phytotoxicity during germination and growth. During growth, lettuce seedlings were subsequently exposed to chlordane (cis-chlordane [CS], trans-chlordane [TC] and trans-nonachlor [TN]) and p,p'-DDE (all at 100 ng/L) in the irrigation solution for a 19-d growth period. CNT exposure did not significantly influence seed germination (82-96%) or plant growth. Similarly, pesticide exposure had no impact on plant growth, total pigment production or tissue lipid peroxidation. After 19 d, the root content of total chlordane and p,p'-DDE was 390 and 73.8 µg g(-1), respectively; in plants not exposed to CNTs, the shoot levels were 1.58 and 0.40 µg g(-1), respectively. The presence and type of CNT significantly influenced pesticide availability to lettuce seedlings. Non-functionalized CNT decreased the root and shoot pesticide content by 88% and 78%, respectively, but amino-functionalized CNT effects were significantly more modest, with decreases of 57% in the roots and 23% in the shoots, respectively. The presence of humic acid completely reversed the reduced accumulation of pesticides induced by amino-functionalized CNT, likely due to strong competition over adsorption sites on the nanomaterial (NM). These findings have implications for food safety and for the use of engineered NMs in agriculture, especially with leafy vegetables.

The combined effects of titanium dioxide (TiO2) nanoparticles and humic acid (HA) on the bioaccumulation of cadmium (Cd) in Zebrafish were investigated. Experimental data on the equilibrium Cd bioaccumulation suggest that only the dissolved Cd effectively contributed to Cd bioaccumulation in HA solutions whereas both the dissolved and TiO2 associated Cd were accumulated in TiO2 or the mixture of HA and TiO2 solutions, due likely to the additional intestine uptake of the TiO2-bound Cd. The equilibrium Cd bioaccumulation in the mixed system was comparable to that in the corresponding HA solutions, and significantly lower than that in the corresponding TiO2 solutions (n=3, p<0.05). The presence of either HA or TiO2 (5-20 mg L(-1)) in water slightly increased the uptake rate constants of Cd bioaccumulation whereas combining HA and TiO2 reduced the uptake rate constants.

Humic acids are compounds resulting from decomposition of organic matter. Despite their common presence, our knowledge of their biological effects is limited, and current findings are controversial. We decided to evaluate the immunological effects of two different types of humic acids, differing in source and biochemical characteristics. Using both components either alone or in combination with the well-established yeast-derived immunomodulator glucan, we measured their effects on both the cellular (phagocytosis and tumor suppression) and humoral (antibody production and cytokine secretion) branches of immune reactions. In summary, our results suggest that humic acids are biologically active immunodulators affecting both the humoral and cellular branches of immune reactions. In addition, the two humic acids studied here are working in synergy in stimulation of the immune reaction, supporting further studies of these natural immunomodulators.

This study provides information on the effects of inorganic and organic constituents on inactivation and sub-lethal injury of Escherichia coli in water stored in a copper vessel. E. coli suspensions were stored for up to 24 h in copper vessels containing one of the following dissolved constituents at 1 g/l: salts of inorganic ions, carbohydrates, proteins and complex natural organic mixtures. Samples were surface plated onto (i) nutrient agar, incubated under standard aerobic conditions to provide conventional counts for uninjured bacteria count and onto (ii) nutrient agar plates with 0.5 g/l sodium pyruvate incubated under anaerobic conditions to enumerate sub-lethally injured (oxygen-sensitive) bacteria alongside their healthy counterparts. The concentration of dissolved copper in the stored water was determined using atomic absorption spectrophotometry. The addition of chloride salts resulted in a faster inactivation of E. coli compared to pure water with no dissolved additives, irrespective of the counterion. In contrast, a slower inactivation was observed in the presence of Na(2)SO(4), NaNO(3) and NaNO(2) when compared to NaCl. Addition of the carbohydrates glucose, lactose and starch gave broadly similar results to those obtained using unsupplemented water. However, the addition of amino acids, proteins, humic acid or complex organic mixtures caused a dramatic decrease in inactivation of E. coli, with evidence of a greater number of sub-lethally injured bacteria than was seen with other added constituents. The amount of copper was highest in stored water containing amino acids and complex organic constituents, with the slow inactivation most likely to be due to complex formation between leached copper and these organic constituents. The present study clearly demonstrates that water composition, particularly natural organic constituents, has a substantial impact on the antibacterial effectiveness and dissolved copper concentration of water stored in copper vessels and that both aspects will need to be considered in terms of their impact on the practical use of copper-based systems for small-scale water treatment.

Interactions of Cu2+, Ni2+ on humic acid and the mixture adsorbent of humic acid and bentonite were studied. The effects of contact time, initial pH and temperature were determined. The removal rate of the metal ions increased with increasing contact time. The adsorption capacities increased with increasing temperature. Initial pH had a great impact on the removal rate of metal ions, when initial pH was around 7, the maximum removal rate can be achieved. Characteristics of adsorption kinetics of Cu2+, Ni2+ from aqueous solutions on humic acid and mixture adsorbent were studied. The results showed that the adsorption process followed the pseudo second-order equation. The activation energy of Cu2+ on humic acid and mixture adsorbent were 17.01 kJ x mol(-1) and 38.49 kJ x mol(-1), and the activation energy of Ni2+ on humic acid and mixture adsorbent were 15.15 kJ x mol(-1) and 13.35 kJ x mol(-1). The activation energy indicated that the adsorption process belonged to physics adsorption. The adsorption process followed the Langmuir isotherm. deltaH0, deltaS0 and deltaG0 calculated showed that the adsorptions of metal ions on humic acid and mixture adsorbent were endothermic, entropy increasing and spontaneous.

The antimutagenic/desmutagenic activity of a leonardite humic acid (LHA) and a soil humic acid (SHA) was studied in the cultured human lymphoblastoid cell line TK6 treated with mitomycin C (MMC) as reference mutagen by evaluating the induction of micronuclei (MN). Two different concentrations of HA were used, 2.5 and 10 microg/ml, in three different treatments: (1) HA alone (genotoxic test); (2) HA after 2-h pre-incubation with 0.3 microM of MMC (desmutagenic test) and (3) combinations of HA and MMC at 0.3 microM without pre-incubation (antimutagenic test). Neither of the HA used alone did produce genotoxic effects, but both HAs reduced significantly the frequencies of MN induced by MMC, especially in the desmutagenic test. A slight cell-protective effect against the cytotoxicity of MMC was also exhibited by the two HAs in the desmutagenic test. The LHA showed a desmutagenic/antimutagenic activity that was more pronounced than that of SHA, which is possibly related to the higher carboxylic group content and lower phenolic group content of LHA. These results confirm the antigenotoxic action exerted by HAs in human cells, similarly to what has been previously observed in various plant species.

Metal speciation in aquatic systems is mainly determined by the type and concentration of ligands present in solution. A very important group of complexing agents is dissolved organic matter (DOM), e.g., humic and fulvic acids. According to the free-ion activity model, only the free metal ion is available to biota. Nevertheless, DOM has been reported to decrease or increase metal uptake, leading to uncertainty concerning the bioavailability of metal-DOM complexes. In this work the effect of Aldrich humic acid on cadmium accumulation by the zebra mussel, Dreissena polymorpha, was studied under laboratory conditions. Mussels, collected in a drinking water reservoir, were exposed to varying environmentally relevant concentrations of cadmium in the presence and absence of humic acid. Cadmium concentrations in the mussel tissues were analyzed, and measurements with a cadmium-ion-selective electrode were made to determine the free cadmium ion activity in the exposure waters. The uptake of humic acid by the zebra mussels was measured by the decrease of the total organic carbon (TOC) concentration in the water over time. The free cadmium ion activity in the water decreased from 51.6% to 19.9% of the total cadmium concentration in the presence of humic acid. This decrease by a factor of 2.6 resulted in a decrease in the cadmium uptake rate in the soft tissue of zebra mussels from 12.9 to 7.9 nmol/g dry wt/day, which corresponds to a decrease by a factor of 1.6. This implies that cadmium uptake rates were higher than predicted by the free-ion activity model and indicates that cadmium-humic acid complexes are partly available to zebra mussels.

Humic acid (HA) has been shown to be a toxic factor for many mammalian cells, however the specific mechanism of the cytotoxicity induced by HA remains unclear. From the assessment of its redox properties, HA has been shown to be capable of reducing iron(III) to iron(II) in aqueous conditions over a broad range of pH values (from 4.0 to 9.0). By using thiobarbituric acid-reactive substances as an index, the presence of HA was noted to increase the extent of lipid peroxidation both for linoleic acids and within rat liver microsomes. In addition, the increase in HA-induced lipid peroxidation is partially inhibited by sodium azide (a singlet oxygen scavenger) or disodium 4,5-dihydroxy-1,3-benzene-disulfonic acid (a superoxide scavenger), reflecting the involvement of singlet oxygen and superoxide in the process of lipid peroxidation. The addition of HA into a reaction system has been shown to generate superoxide in a dose-dependent manner by the superoxide dismutase-inhibitable cytochrome c reduction assay. In addition, HA is able to reduce and release iron from ferritin, but this process is partially inhibited by superoxide scavengers. Subsequently, the iron released from ferritin was shown to accelerate the HA-induced lipid peroxidation. From our results we conclude that HA has the ability to reduce and release iron from ferritin storage as well as to promote lipid peroxidation. Therefore, HA coupled with released iron can disturb the redox balance and elicit oxidative stress within a biological system. This may be one of the most important mechanisms for HA-induced cytotoxicity.