Soluble Humic-like Substances Research Articles

Light absorption and source apportionment of water soluble humic-like substances (HULIS) in PM2.5 at Nanjing, China

Humic-like substances (HULIS), as important components of brown carbon (BrC), play an important role in climate change. In this study, one-year PM2.5 samples from 2017 to 2018 were collected at Nanjing, China and the water soluble HULIS and other chemical species were analyzed to investigate the seasonal variations, optical properties and possible sources. The HULIS concentrations exhibited highest in winter and lowest in summer. The annual averaged HULIS concentration was 2.61 ± 1.79 μg m−3, accounting for 45 ± 13% of water-soluble organic carbon (WSOC). The HULIS light absorption coefficient at 365 nm (Abs365, HULIS) averagely accounted for 71 ± 19% of that of WSOC, suggesting that HULIS are the main light-absorbing components in WSOC. The annual averaged Ångström absorption exponent and mass absorption efficiency of HULIS at 365 nm were 5.22 ± 0.77 and 1.71 ± 0.70 m2 g−1. Good correlations between HULIS with levoglucosan and K+ suggested biomass burning (BB) influence on HULIS. High concentrations of HULIS and secondary species (e.g., NO3−, SO42−, NH4+, C2O42−) were found in present of high relative humidity, indicating strong aqueous phase secondary HULIS formation. Secondary HULIS produced from anthropogenic and biogenic precursors were quantified based on the positive matrix factorization (PMF) model and the results showed that both fossil (55%) and biogenic (45%) emission sources made great contributions to HULIS. Fossil fuel combustion significantly contributed to HULIS formation throughout the whole year, which were enriched with more secondary HULIS (30%) than primary HULIS (25%). Strongest BB contribution (39%) was found in winter and biogenic SOA contribution (32%) was found in summer. A multiple linear regression (MLR) method was further applied to obtain specific source contributions to Abs365, HULIS and the results showed that strong light-absorbing chromophores were produced from anthropogenic precursors. Our results highlight the anthropogenic SOA and fossil fuels combustion contributions to HULIS in addition to the biggest contributor, BB, in urban area in China.

Quality of heavy metal-contaminated soil before and after column flushing with washing agents derived from municipal sewage sludge

Removal of heavy metals (HMs) from soil is a priority in soil washing/soil flushing. However, for further management of remediated soil, it should be characterized in detail. This study presents, for the first time, an evaluation of soil quality after column flushing with new-generation washing agents (WAs) recovered from municipal sewage sludge (dissolved organic matter, DOM; soluble humic-like substances, HLS; soluble humic substances, SHS) and Na2EDTA as a standard benchmark. Sandy loam soil was spiked with industrial levels of Cu, Pb and Zn, then flushed in a column reactor at two WA flow rates (0.5 and 1.0 ml/min). Soil quality was assessed by determining both physico-chemical (pH, total HMs and their mobility, soil organic matter, OM, humic substances, HS and their fractions, macroelements) and biological indicators (dehydrogenase activity, DHA; germination rate, GR; and inhibition factors for roots and shoots of Triticum aestivum). Total residual HMs contents and HMs contents in the mobile fraction were significantly lower in soil flushed at 1.0 ml/min than in soil flushed at 0.5 ml/min. With all WAs, the decrease in Cu content was larger than that of the other HMs, however this HM most effectively was removed with DOM. In contrast, Pb most effectively was removed by HLS and Na2EDTA, and DOM should not be used to remediate Pb-contaminated soil, due to its very low effectiveness. Flow rate did not appear to affect the fertilizing properties of the soil, DHA activity or soil toxicity indicators. Soil flushing with all SS_WAs increased OM, HS, and exchangeable P, K and Na content in remediated soils, but decreased exchangeable Ca content, and in most cases, exchangeable Mg content. Soil flushing substantially improved DHA activity and GR, but only slightly improved the shoot and root inhibition factors.

A holistic approach to remediation of soil contaminated with Cu, Pb and Zn with sewage sludge-derived washing agents and synthetic chelator

Green soil washing is a new trend in remediation of heavy metal (HM) contaminated soils that is based on application of washing agents (WAs) derived from organic waste sources. This study compared for the first time the efficiency of sewage sludge-derived WAs (SS_WAs) (dissolved organic matter, DOM; soluble humic-like substances, HLS; soluble humic substances, SHS) extracted from sewage sludge with water or a NaOH solution. As a benchmark for comparison, Na2EDTA was used. The FT-IR/PAS spectra had higher intensities for SS_WAs than Na2EDTA, with a predominance of carboxyl groups in all WAs. The WAs were used to remove Cu, Pb and Zn from soil during double batch washings. The effects of these WAs on HM removal and the quality of remediated soil, including fertility indicators, content of humic substances, HM distribution, HM stability, soil phytotoxicity and activity of soil microorganisms (as dehydrogenase activity, DHA) were evaluated. The SS_WAs removed HMs with high efficiency (HLS 80–90%, SHS 61–89%), although slightly less efficiently than Na2EDTA (93–95%). DOM very efficiently removed Cu (7274 mg Cu·kg−1), but not Pb. Soil washing affected changes in HM distribution by increasing stability of most HM in washed soil. All SS_WAs, in contrast to Na2EDTA, increased soil content of organics and nutrients. The type of WA had no effect on germination of wheat seeds. However, Na2EDTA inhibited shoot and root growth (by 0.6% and 33%, respectively) and only slightly increased DHA in washed soil. In contrast, all SS_WAs stimulated shoot growth (by 29.4–40.6%), and HLS and SHS also stimulated root growth (by 5.6–11.6%) and increased DHA by the largest amount (6.5–7.4-fold compared to unwashed soil). Sewage sludge constitutes an important waste source of easily obtainable SS_WAs, which possess great potential for remediating highly polluted soils, especially Cu-polluted soils, with low toxicity and recovery of soil function. In conclusion, this holistic assessment of soil remediation indicates that SS_WAs can be an attractive alternative to Na2EDTA.

Kinetics of Cu, Pb and Zn removal during soil flushing with washing agents derived from sewage sludge

This paper presents the first tests of Cu (7875 mg/kg), Pb (1414 mg/kg) and Zn (566 mg/kg) removal from contaminated soil with sewage-sludge–derived washing agents (SS_WAs) (dissolved organic matter, DOM; soluble humic-like substances, HLS; soluble humic substances, SHS) and Na2EDTA (as a standard benchmark) in column experiments. Flow rates of 0.5 ml/min and 1 ml/min were used. Using a 1. order kinetic model, the kinetic constant (k), the maximum concentrations of each metal removed (Cmax), and the initial rates of metal removal (r) were established. At both flow rates, stable flow velocity was maintained for approximately eight pore volumes, for flushing times of 8 h (1.0 ml/min) and 16 h (0.5 ml/min). Although the flow rate did not influence k, it influenced Cmax: at 1 ml/min, Cmax values were higher than at 0.5 ml/min. For Cu and Zn, but not Pb, k was about twofold higher with Na2EDTA than with SS_WAs. Although Na2EDTA gave the highest kCu, Cmax,Cu was highest with DOM (Na2EDTA, 66%; DOM 73%). For Pb removal, HLS was the most effective SS_WA (77%; Na2EDTA was 80% effective). kZn was about twofold higher with Na2EDTA than with SS_WAs. Cmax,Zn was highest with HLS. The quick mobilization of Cu, Pb and Zn with most of the WAs corresponded to efficient metal removal from the exchangeable (F1) fraction.

Washing agents from sewage sludge: efficiency of Cd removal from highly contaminated soils and effect on soil organic balance

PurposeTo compare Cd removal from different soils with three washing agents recovered from sewage sludge (dissolved organic matter (DOM), soluble humic-like substances (HLS), soluble humic substances (SHS)). Also, to investigate how washing with these agents changes soil organic-matter composition (OM).Materials and methodsSandy clay loam (S1) and clay (S2) highly contaminated with Cd (300 mg kg−1) were washed with DOM, HLS, or SHS solutions at various pHs, and with various washing times and washing modes (single or double). Cd distribution and OM composition were determined (including content of humic substances (HS), fulvic fraction (FF), labile humic acids (L-HA), and stable humic acids (S-HA)).Results and discussionCd removal proceeded with pseudo-second-order kinetics. Equilibrium was reached in 30 min (S1) and 60 min (S2). DOM, HLS, and SHS removed 75–82% of Cd from S1, and 80–87% from S2. The most mobile fraction of Cd was removed after one wash. S2 retained more OM, including HS, than S1. Although washing did not change the HA/FF ratio in most variants, washing with DOM and HLS increased the percentage of L-HA in both soils. Washing with SHS increased S-HA content in both soils, but the percent content of S-HA was similar to that in the unwashed soil.ConclusionsDOM, HLS, and SHS derived from sewage sludge can effectively remediate clay and sandy clay soils highly contaminated with Cd. Washing with an SHS solution can increase the content of the most stable carbon forms (HA), which is beneficial for carbon sequestration in remediated soils.

Abundance and 14C-based source assessment of carbonaceous materials in PM2.5 aerosols in Guangzhou, South China

In this study, the carbonaceous aerosols were separated into organic carbon (OC), water soluble OC (WSOC), water soluble humic-like substances (HULIS), water soluble non-HULIS, water insoluble OC (WINSOC), and soot carbon (SC). Then the abundance and 14 C content of carbon fractions were determined to assess the contribution of contemporary versus fossil sources. The results showed that the OC fraction is the major carbon fraction, the OC sub-fractions such as WSOC, HULIS, non-HULIS, and WINSOC accounted for 39.5%–66.7%, 24.8%–43.2%, 11.9%–23.5%, and 31.3%–55.2% of total carbon (TC), respectively. The 14 C data show that the contribution of contemporary carbon ( f c ) to TC is 38.3%–63.5%, all carbon fractions were mixtures of carbon derived from contemporary and fossil sources. The f c values of OC (38.8%–63.9%) more than that (25.7%–46.6%) of SC in the same sample, indicated OC generally contained more contemporary carbon than SC. The WSOC and HULIS had relatively higher f c levels than the corresponding WINSOC and the f c values of WINSOC all less than 45%, indicated that the insoluble organic fractions in PM 2.5 samples were dominated by fossil fuel related sources. These results suggested that the contemporary and fossil contributions for different carbon fractions are different. In addition, the seasonal and spatial variations of contemporary and fossil contributions to carbon fractions indicated that the PM 2.5 samples collected during summer at background site (Maofengshan, MFS) and winter at urban site (Wushan, WS) have relative high contribution from contemporary sources, suggested the differences of primary and secondary sources at the two sites. • 14 C-based source assessment of carbonaceous materials in PM 2.5 aerosols. • All carbon fractions are mixtures of contemporary and fossil carbon. • The source of carbon fractions in aerosols is heterogeneous.

Temporal variations of the abundance and optical properties of water soluble Humic-Like Substances (HULIS) in PM2.5 at Guangzhou, China

Humic-Like Substances (HULIS) are important macromolecular compounds that are present in PM2.5 and play significant roles in the atmospheric environment. In this study, 48 PM2.5 samples were collected from February 2010 to January 2011 at an urban site in Guangzhou, southern China. The water soluble HULIS fractions in PM2.5 were analyzed to explore the temporal variation of abundance and optical properties and to identify their possible sources. The HULIS concentrations were in the range of 0.4 to 8.2μgCm−3, with a mean of 2.4μgCm−3. HULIS are important components in organic aerosols, accounting for 17±5% of the organic carbon (OC), and 49±6 and 68±5% of water soluble organic carbon (WSOC) as determined with a total organic carbon (TOC) analyzer and UV absorbance at 250nm, respectively. The special UV absorbance (SUVA) at 254nm and 280nm and the E250/E365 ratio of HULIS were 3.2±0.5L (mmgC)−1, 2.2±0.4L (mmgC)−1, and 5.9±0.9, respectively. The HULIS fractions had higher concentrations, slightly higher SUVA values, and lower E250/E365 ratios from November to January, indicating the important contribution of aromatic compounds to HULIS in the dry season. The concentrations of HULIS were positively correlated with water soluble K+, secondary organic carbon (SOC), and secondary inorganic ions (NH4+, NO3−, and SO42−). These results suggest that biomass burning and secondary photochemical formation are both sources of HULIS in our study area. In addition, the SUVA280 of HULIS was strongly correlated with K+ and SOC, suggesting that HULIS properties were also influenced by their primary source of biomass burning and secondary atmospheric formation.

Efeito de substâncias húmicas na cinética de absorção de potássio, crescimento de plantas e concentração de nutrientes em Phaseolus vulgaris L.

As substâncias húmicas podem influenciar direta ou indiretamente o metabolismo das plantas, alterando assim o seu crescimento. O objetivo deste trabalho foi avaliar o efeito de substâncias húmicas (SH) no crescimento e na concentração de nutrientes em plantas de feijão (Phaseolus vulgaris, L.) e nos parâmetros cinéticos de absorção de K. O experimento foi realizado em bancada de laboratório, com luz artificial. As plantas cresceram em vasos contendo solução nutritiva completa acrescida de cinco doses (0; 2,5; 5; 10; e 20 mg L-1 de C) de SH solúveis em meio alcalino (ácido húmico + ácido fúlvico), extraídos de amostra de carvão mineral da mina de Candiota, RS, da Companhia Riograndense de Mineração, num delineamento completamente ao acaso, com três repetições. Aos 28 dias de cultivo, foram avaliados parâmetros cinéticos de absorção de K, massa da parte aérea e da raiz seca, teores de N, P, K, Ca e Mg no tecido da parte área e as características morfológicas de raízes (comprimento, área e raio). Os resultados evidenciaram que a adição de SH extraída de carvão mineral estimulou o crescimento do feijão e afetou a cinética de absorção de K. A produção de massa da parte aérea seca das plantas mostrou resposta quadrática à adição de substâncias húmicas, atingindo valor máximo na dose equivalente a 11 mg L-1 de C, enquanto a massa das raízes secas aumentou linearmente em até 41 %, com as doses testadas. As características morfológicas de raiz e o estado nutricional das plantas não foram significativamente afetados pelas SH. Os parâmetros cinéticos de absorção de K, Imáx, Cmín e Km, decresceram linearmente com o aumento das doses de SH, causando redução na taxa de absorção de K nas concentrações deste nutriente na solução superiores a 10 μmol L-1.

Extractable iron and organic matter in the suspended insoluble material of fog droplets

In this work the formation and composition of aggregates between metals and organic material is studied in real fog samples. In a preliminary experiment it has been found that concentrated cloud samples form a yellow-brown precipitate in the presence of Fe(III). Standards of humic acids and fulvic acids co-precipitate with Fe(III), forming similar aggregates i.e. iron-humates (Fe-HA) and iron-fulvates (Fe-FA). By comparing the solubility properties of aggregates by extracting organic carbon (OC) in different pH conditions, it has been observed that fog droplet particulate samples are characterised by solubility properties more similar to those of Fe-HA than Fe-FA. Dilute alkaline solutions can also easily extract organic refractory substances that form aggregates with metals. The recoveries of the total extractable organic matter (accounting for 12% of total insoluble carbon and 15% of particulate mass) are similar to those of humic-like substances (HULIS) from particulate samples. The chromatographic behaviour and functional group characteristics measured in the alkali-extract fraction of precipitated aggregates with iron and in the insoluble particulate of fog samples, are those of humic-like material. Thus, soluble HULIS are able to interact with iron to form particulate, but the composition of a large fraction of insoluble organic carbon is still unknown. These findings have implications on the solubility and surface tension properties of fog droplets and can therefore potentially influence droplet formation, as well as cloud chemical and photochemical processes.

Characterization of high molecular weight compounds in urban atmospheric particles

Abstract. The chemical nature of a large mass fraction of ambient organic aerosol particles is not known. High molecular weight compounds (often named humic-like substances) have recently been detected by several authors and these compounds seem to account for a significant fraction of the total organic aerosol mass. Due to the unknown chemical structure of these compounds quantification as well as a determination of their molecular weight is difficult. In this paper we investigate water soluble humic-like substances in ambient urban aerosol using size exclusion chromatography-UV spectroscopy and laser desorption/ionization mass spectrometry (LDI-MS). LDI-MS was used for the first time to investigate HULIS from atmospheric aerosols. A careful evaluation of the two method shows that both methods complement each other and that both are needed to learn more about the molecular weight distribution and the concentration of humic-like substances. An upper molecular weight limit of humic-like substances of about 700 Da and a concentration of 0.3-1.6 µg/m3 air can be estimated, corresponding to 9-30% of the total organic carbon for an urban background site.