Processes affecting the fate of mercury in the Krka River Estuary

The concentrations of reactive and total mercury (in the u.v.-irradiated samples) were measured in the Krka River Estuary during the period from April 1988 to February 1991. Salinity, temperature, pH_NBS, calcium and magnesium were also measured. Only calcium and magnesium ions exhibited a linear conservative dilution property. Temperature measurements indicated a subsurface warming just below the freshwater-seawater interface (FSI) in spring and temperature inversion in winter. pH_NBS profiles showed different patterns with variations up to one pH unit. The concentrations of reactive and total mercury, exhibiting different patterns, present a “momentum situation” and suggest composite scavenging processes.The fate of mercury in the Krka River Estuary is highlighted and qualitatively described as follows:

• - from increased surface mercury concentrations after a heavy rain, an atmospheric mercury input has been suggested

• - mercury species in the freshwater layer are chiefly connected with organic material

• - the adsorption of mercury at the FSI can occur on at least some of the mineral surfaces found at the FSI and identified in this work. (The identified phases are: calcite, quartz, calcium silicate hydrate and takanelite)

• - transport of mercury to sediments occurs, during calm weather, by sedimentation of particulates with the adsorbed mercury, and during a storm, by a wind-induced vertical gyre within the marine layer. The seawater at the bottom is replaced with the seawater from the FSI which accumulates organic material. Consequently, mercury is bound more to the organic material than to the inorganic complexes.

The difference in total and reactive mercury concentrations observed in the whole vertical profile after the Bura wind, shows that mercury is bound to organic material on that occasion. This difference could be used as a useful parameter for observation of the vertical mixing in the seawater layer in the Krka River Estuary during a storm.     

Influence des substances organiques dissoutes sur le dosage du plomb en milieu marin par redissolution anodique

Lead is usually determined at pH 2 in seawater by differential pulse anodic stripping voltammetry. At such a pH however, the peak of lead is not well resolved at the hanging mercury drop electrode. Batley and Florence (1976) attribute this phenomenon to the organic matter dissolved in sea water, whereas Acebal and De Luca Rebello (1983) ascribe it to the copper dissolution with oxidation to CuCl₂⁻. The objective of this work is hence to know: (1) which of these two hypotheses is right and (2) if a hanging mercury drop electrode can be used for the determination of lead in coastal seawaters.In the first section, we have studied the effects of physicochemical (concentration, acidity) and electrochemical (deposition potential) parameters on the stripping voltammetry of lead (Figs 1–3). The anodic stripping peak at pH 2 is highly modified by the presence of an interference peak at nearly the same potential; on the other hand when the sample is irradiated under ultraviolet light this “double wave” disappears to give rise to a well resolved peak (Figs 4 and 5). We have shown that the phenomenon was related to the influence of dissolved organic matter.Anodic stripping voltammetry must be used with care because, in some pH conditions, natural organic compounds like humic and fulvic acids give rise to adsorption waves which may cause an increase or a decrease in the peak heights introducing errors on the lead concentration.In the last part, the best experimental conditions to determine lead concentrations have been investigated. They are obtained when the samples are acidified and u.v. irradiated. In these conditions, anodic stripping voltammetry and atomic absorption spectrophotometry are in good agreement. It appears that if the sample is not treated as proposed, anodic stripping voltammetry at a hanging mercury drop electrode, at pH 2, gives erroneous results in excess for lead dissolved in seawater.     

Automated determination of carbon in natural waters

An automated method for determining inorganic carbon and organic carbon in water is described. The sample is acidified and the CO₂ from inorganic carbonate is removed in a packed column and measured with an i.r. analyzer. The stripped liquid is pumped to a furnace containing cobalt oxide catalyst at 950°C where the organic carbon is oxidized; the resulting CO₂ is measured with an i.r. analyzer. Operating as a “two-channel” system, inorganic carbon and organic carbon are measured simultaneously at 20 samples per hour. If used in a “single-channel” mode, inorganic and organic carbon are measured separately, inorganic carbon at 60 samples per hour, organic carbon at 20 samples per hour. The coefficients of variation at 1 and 5 mg l⁻¹ organic carbon are 5.1 and 2.8% respectively. The detection limit is 200 μg l⁻¹C.     

Addition of NaOH, limestone slurry and finegrained limestone to acidified lake water and the effects on smolts of atlantic salmon (Salmo salar L.)

A neutralization experiment comparing NaOH, limestone slurry and finegrained limestone was performed using smolts of Atlantic salmon as testfish. Smolts were raised on chronically acid Lake Liervatn (pH = 4.9–5.4, conductivity = 55 μ S cm⁻¹, Ca = 1.3 mg l⁻¹, labile Al = 40 μg l⁻¹). As a result testfish were sublethally stressed prior to the experiment, as indicated by low levels of plasma chloride. During the experiment, smolts were held in keepnets in the middle of large plastic enclosures without sediment contact. Rapid changes in pH and Al-speciation were recorded after addition of the neutralizing agents. No mortality of fish occurred during the 3 days exposure. Plasma chloride levels in fish exposed to limestone slurry, limestone and the lowest concentration of NaOH (pH = 5.9) did not differ significantly from levels in fish from the reference group. Fish exposed to the highest concentration of NaOH (pH > 7.45), however, experienced a significant decrease in plasma chloride levels. Increased sublethal stress in treatments with NaOH was presumably caused by the presence of aluminate ions [Al(OH)₄⁻] at high pH and by low concentrations of Ca. The importance of maintaining pH below 7 when using bases with monovalent cations is emphasized. Adding inorganic aluminium to the lake water induced loss of plasma chloride within 48 h at 70 μg labile Al l⁻¹ at pH 5.1 and 1.2 mgCa l⁻¹.     

Mercury in the river mersey, its estuary and tributaries during 1973 and 1974

Mercury levels found in waters and suspended matter from 53 stations, occupied four times at 3-monthly intervals, showed that most mercury was associated with particulates but the amount varied during the year. In the polluted region between Warrington and Runcorn, where fresh-water and sea-water converge, >80% of the mercury was associated with the particulates. Dissolved mercury concentrations and the mercury load on particulate matter were always greater in freshwater than in tidal waters, except during a flood. A model of partitioning of mercury between particulate and dissolved phases is presented. The River Weaver and the Manchester Ship Canal were grossly polluted with mercury throughout that year due to a Castner-Kelner plant at Runcorn. Dredge spoils and water flow transport 17 (range 8–138) and 1.55 ± 65% tonnes yr⁻¹ respectively of mercury into Liverpool Bay.     

Conditions required for the precipitation of aluminium in acidic natural waters

Laboratory and field studies were carried out in order to define the conditions necessary for the precipitation of Al in natural waters of pH 4–6. It is concluded that if precipitation does occur it involves the formation of Al(oxy)hydroxide, not aluminosilicates or basic aluminium sulphates. The solubility product of the Al(oxy)hydroxide is highly temperature dependent (ΔH = −30.5 kcal⁻¹). It is also sensitive to concentrations of SO₄²⁻ and, more markedly, humic substances (HS); both of these decrease solubility, HS by more than an order of magnitude at a concentration of approx. 5 mg l⁻¹ (equivalent to approx. 2.5 mg l⁻¹ dissolved organic carbon). A semi-empirical equation is proposed that allows the prediction of the effective solubility product at different temperatures and at humic concentrations in the range 0–7 mg l⁻¹. Of the 113 natural water samples analysed, only one was calculated to be oversaturated with respect to Al(oxy)hydroxide.     

Mercury distribution in waters and fishes of the upper Madeira rivers and mercury exposure in riparian Amazonian populations

In this paper, the results of mercury concentrations in two abiotic compartments (river water and suspended particles) and two biotic compartments (fish and human hair) from the upper Madeira rivers of the Bolivian Amazon basin are presented. Because of the local hydrological regimes and a high deposition rate in the plain, due to the presence of a subsidence zone at the bottom of the Andean piedmont, in the dry season, the highest mercury concentrations and fluxes were not found in rivers where mining activities took place (2.25–6.99 ng l⁻¹; and 1.07–8.67 mg Hg d⁻¹ km⁻²), but at the outlet of the Andean basins exploited for their alluvial gold (7.22–8.22 ng l⁻¹; and 9.47–9.52 mg Hg d⁻¹ km⁻²). The total mercury concentrations measured in surface waters of the upper Beni basin varied during the dry season, from 2.24 to 2.57 ng l⁻¹ in the glacial waters of the Zongo river, to 7.00 ng l⁻¹ in the Madeira River at Porto Velho and 9.49–10.86 ng l⁻¹ at its confluence with the Amazon. The results obtained from fish indicate, on one hand, that 86% of the piscivorous fishes collected in the Beni river were contaminated, and, on the other hand, their high mercury concentrations could exceed by almost four times the WHO (1976) safety limit. In the Beni River, the mercury concentrations found in omnivorous and mud-feeding fish ranged from 0.02 to 0.19 μg g⁻¹ (wet wt.), and in piscivorous fish, from 0.33 to 2.30 μg Hg g⁻¹ (wet wt.). The mercury accumulated by carnivorous fishes was mainly present in its organic form; methylmercury represented 73–98% of the total mercury analysed. Eighty persons were studied in the entire Bolivian Amazonian basin. Unlike the gold miners, who are more affected by tropical diseases, such as malaria and yellow fever, the indigenous people living on the banks of the Beni river, present elevated levels of mercury (9.81 μg g⁻¹ on average). We observed an increase in contamination in young children still being breast-fed, confirming that hair mercury concentration in babies was significantly affected by maternal mercury contamination during pregnancy. These results show that the major health impacts caused by mercury affect people who are not working directly in gold mining activities but who have a regular fish diet.     

The complexation of protons, aluminium and calcium by aquatic humic substances: A model incorporating binding-site heterogeneity and macroionic effects

A model is presented that describes the competitive binding of protons and metal ions (Al³⁺, AlOH²⁺, Ca²⁺) by humic substances (HS) in the pH range 3–6 and at different ionic strengths, and allows the net humic charge to be calculated. The HS are treated in terms of two types of carboxyl group, together with other more weakly-acidic groups, and the influence of humic (macroionic) charge is taken into account. Eight parameters are involved: total humic acidity, which can be measured directly, content of COOH groups, 4 intrinsic equilibrium constants (2 for H⁺ binding, 2 for metal binding), and 2 parameters accounting for charge effects at different ionic strengths. The model was applied to 4 aquatic humic samples, parameters being estimated from acid-base titration data. The equilibrium contents did not vary greatly among the humic samples, which is consistent with the idea that the functional groups in each sample are chemically the same. The effect of humic charge on complexation varies considerably among the samples. The model was reasonably successful at predicting humic-bound Al in laboratory-prepared solutions and field samples. Calculations based on the model suggest that, (1) Ca²⁺ does not compete significantly with Al for binding to HS under natural acid conditions, and (2) that there is a direct relationship between humic solubility and net humic charge.     

Aluminium complexation by an aquatic humic fraction under acidic conditions

Equilibrium dialysis and acid-base titration were used to investigate the interactions between Al and a fraction of aquatic humic substances (HS), in the pH range 3–5. Binding of Al by the HS increased with Al³⁺ activity and with pH. Under conditions relevant to natural waters, υ (mol Al bound per gHS) varied from 0 to 1.5 × 10⁻³. The data were modelled with an emprical linear logarithmic expression (Model I) and on the basis of the polyelectrolyte nature of the HS, incorporating competitive binding of H⁺ and Al³⁺ (Model II). Both models gave tolerable fits (r = 0.93). Model I is simpler to apply, while Model II allows the calculation of proton release accompanying Al binding, and provides information on the net charge of the Al---HS complexes. The results were used to calculate the distribution of Al between organic and inorganic forms under conditions prevailing in acidic natural waters.     

Electroflottation et desinfection simultanee d'eaux residuaires urbaines

This reports presents the results of a simultaneous electroflotation and disinfection sewage treatment, after chemical coagulation and flocculation and in the presence of chloride ions at various concentrations. Theoretical studies had shown that anodic oxidation of chloride ions gives hyperchlorites (for pH 7.5) together with (if sufficient potential is provided) oxygen. A dynamic study was thus achieved. It appeared that for a given chloride concentration the chlorine production linearly increases with the current density and depends on the organic load (COD) and oxidation potential of the effluent (Figs 6, 7 and 8). The performances of the process were studied in the continuous mode on a small pilot plant, after treatment of the effluent with ferric chloride and an organic polymer (Fig. 2). In all experiments current density and chloride concentration were raised (respectively 100, 200, 300 A m⁻² and from 300 to 3000 mg l⁻¹). The results obtained showed that solid-liquid separation was improved over static clarification for 2 h (Table 3) and the disinfection efficiency was equal or better than that obtained with gaseous chlorine (Table 4, Fig. 9). For example at a 900 mg l⁻¹ chloride concentration the three current density used give treated water containing less than 10³/100 ml total coliforms (initial concentration 4.7 · 10⁷/100 ml). These results have direct applications to the design of electroflotation units where a better plug flow should be sought. Moreover this process produces highly concentrated sludges. The utilization of ATP (Adenosine Triphosphate) as an indicator of the viability of a biomass showed that the process is applicable to activated sludges with recycling. The experimental conditions required for this application are still uncertain and require further study.     

Speciation and rate of loss of copper from lakewater with implications to toxicity

The rates of disappearance of total dissolved copper in six prairie “pothole” hard water lakes treated with copper were measured. The first-order rate constants ranged from 1.01 to 0.11 day⁻¹, and the half-times from 1 to 7 days. Concentrations of 12 inorganic copper species and the humic acid-copper complex were calculated for the pH range of each lake. Less than 0.5% of total dissolved copper was calculated to be present at any time as free cupric ion. The total dissolved concentration of added copper was reduced with time probably through precipitation of tenorite (in some cases malachite) and by adsorption on solids.The effectiveness of copper as an algicide in these lakes at the relatively low concentration of added copper is explained in terms of a “total toxic copper” concept, which includes the species Cu(OH)₂⁰ and CuOH⁺ in addition to cupric ion, the generally recognized toxic species.     

Particle formation and growth in dilute aluminum(III) solutions : Characterization of particle size distributions at pH 5.5

Particle formation and growth over the 1–40 μm size range in dilute aluminum solutions (approx. 2 × 10⁻⁴ M) have been studied using an electronic particle counter. Sulfate, fulvate and hydroxide ion accelerate the rate of particle formation and changes of the particle size distribution over time. Increasing ionic strength (inert electrolyte) produces similar but less dramatic effects. Combinations of sulfate and fulvic acid or sulfate and inert electrolyte further accelerate the rate of particle formation. Aluminum chloride solutions at moderate ionic strength are devoid of supramicron particles after several days. A conceptual pathway model is developed which suggests that two different solids are formed when aluminum is added to fulvic acid solutions: an aluminum-fulvate precipitate and Al(OH)₂(s). The first solid dominates in fulvic acid solutions at pH 5.5.     

Total mercury and methyl mercury levels in British estuarine sediments—II

Results from a large-scale study of Mersey Estuary, U.K. sediments are discussed. Correlations are drawn between total mercury, methyl mercury, silt and organic carbon contents of the sediments. These correlations are compared to earlier results, and coefficients range from 0.55 to 0.94.The influence of redox potential and the sulphide content of a sediment on both the ambient level of methyl mercury and the extent of a growth and decay effect in methyl mercury levels in sediments after sampling is discussed. The results show that in an esturary (Clyde, U.K.) where sulphide levels vary from 0 to 8.5 mg g⁻¹ there is a maximum level of methyl mercury found at approximately 5.8 mg g⁻¹ sulphide, suggesting that sulphide concentrations may control methyl mercury levels.     

Removal of As(III) and As(V) by Tin(II) compounds

The retention capacity for arsenic species of new nanomaterials based on tin(II) inorganic oxides or hybrid (inorganic and organic) materials was studied. The synthesis of a polymer-metal complex was performed with poly(acrylic acid) and tin(II) chloride. Poly(AA)-Sn(II) with 10 and 20 wt% of tin and a structure with a mol ratio tin:carboxylate group of 1:1, were characterized. These compounds with 10 and 20 wt% of tin content were used to compare the arsenic removal capability through the liquid-phase polymer-based retention, (LPR), technique. Also, tin oxide was prepared by adding alkaline solution to tin(II) chloride salt. The intermediate tin compound was studied by UV-Vis spectroscopy at different pH values and quantified by potentiometric titration. The solid structure is characterized by Fourier transformed infrared spectroscopy, X-ray diffraction, and specific area BET (N₂). Removal of arsenite and arsenate species from solution by hydrolysated tin was carried out by LPR technique with ultrafiltration membranes and a fixed-bed column unsupported or supported on SiO₂. In all these cases, a washing method at constant pH was applied. The arsenic retention ability depended on the class of tin compounds prepared, with a higher efficiency for arsenic being observed at basic pH for soluble complex poly(AA)-Sn(II) than that for tin hydroxide or hydrolysate of Sn⁺².     

Oxidative removal of aqueous steroid estrogens by manganese oxides

This study investigated the oxidative removal of steroid estrogens from water by synthetic manganese oxide (MnO₂) and the factors influencing the reactions. Using 1 × 10⁻⁵ M MnO₂ at pH 4, estrone (E1), 17β-estradiol (E2), estriol (E3) and 17α-ethinylestradiol (EE2), all at 4 × 10⁻⁶ M, were rapidly removed within 220 min, indicating the effectiveness of MnO₂ as an oxidizing agent towards estrogens. E2 removal increased with decreasing pH over the tested range of 4-8, due most likely to increased oxidizing power of MnO₂ and a cleaner reactive surface in acidic solutions. Coexisting metal ions of 0.01 M (Cu(II), Zn(II), Fe(III) and Mn(II)) and Mn(II) released from MnO₂ reduction competed with E2 for reactive sites leading to reduced E2 removal. Observed differential suppression on E2 removal may be related to different speciations of metals, as suggested by the MINTEQ calculations, and hence their different adsorptivities on MnO₂. By suppressing the metal effect, humic acid substantially enhanced E2 removal. This was attributed to complexation of humic acid with metal ions. With 0.01 M ZnCl₂ in solutions containing 1 mg l⁻¹ humic acid, the binding of humic acid for Zn(II) was determined at 251 mmol g⁻¹. An in vitro assay using human breast carcinoma MCF-7 cells indicated a near elimination of estrogenic activities without secondary risk of estrogen solutions treated with MnO₂. Synthetic MnO₂ is therefore a promising chemical agent under optimized conditions for estrogen removal from water. Metal chelators recalcitrant to MnO₂ oxidation may be properly used to further enhance the MnO₂ performance.     

Influences of humic acid, bicarbonate and calcium on Cr(VI) reductive removal by zero-valent iron

The influences of various geochemical constituents, such as humic acid, HCO₃⁻, and Ca²⁺, on Cr(VI) removal by zero-valent iron (Fe⁰) were investigated in a batch setting. The collective impacts of humic acid, HCO₃⁻, and Ca²⁺ on the Cr(VI) reduction process by Fe⁰ appeared to significantly differ from their individual impacts. Humic acid introduced a marginal influence on Fe⁰ reactivity toward Cr(VI) reduction, whereas HCO₃⁻ greatly enhanced Cr(VI) removal by maintaining the solution pH near neutral. The Cr(VI) reduction rate constants (k_obs) were increased by 37.8% and 78.3%, respectively, with 2 mM and 6 mM HCO₃⁻ in solutions where humic acid and Ca²⁺ were absent. Singly present Ca²⁺ did not show a significant impact to Cr(VI) reduction. However, probably due to the formation of passivating CaCO₃, further addition of Ca²⁺ to HCO₃⁻ containing solutions resulted in a decrease of k_obs compared to solutions containing HCO₃⁻ alone. Ca²⁺ enhanced humic acid adsorption led to a minor decrease of Cr(VI) reduction rates. In Ca²⁺-free solutions, humic acid increased the amount of total dissolved iron to 25 mg/l due to the formation of soluble Fe-humate complexes and stably dispersed fine Fe (oxy)hydroxide colloids, which appeared to suppress iron precipitation. In contrast, the coexistence of humic acid and Ca²⁺ significantly promoted the aggregation of Fe (oxy)hydroxides, with which humic acid co-aggregated and co-precipitated. These aggregates would progressively be deposited on Fe⁰ surfaces and impose long-term impacts on the permeability of PRBs.     

Time-dependent variation of mercury in a stream sediment and the effect upon mercury content in Gammarus pulex (L.)

A 3-month investigation has been carried out in a stream environment, on the fluctuation of the level of mercury within the sediment and the Gammarus pulex population. A positive correlation is found between the organic content and the mercury content (μg g⁻¹ dry wt) of the samples. The mean mercury concentration in the organic fraction can be read from the regression line. Of the units: μg g⁻¹ dry wt, μg g⁻¹ ashfree dry wt and μg cm⁻³, the values expressed g⁻¹ ashfree dry wt are considered to be of greatest validity for comparing different localities, and for establishing the pollution level in a stream sediment. Within the investigation period a very high fluctuation is found in the mercury content of analyzed Gammarus pulex. The phenomenon may be explained through fluctuations in the methylating processes within the sediment. No positive correlation is found between mercury in Gammarus pulex and in sediement taken from identical sample locations.     

Adsorption des acides humiques sur charbon active en poudre. Influence du triphosphate de sodium

The use of activated carbon beds for the removal of natural humic and fulvic substances found in water supplies, has recently received considerable attention in water treatment operation (Lee et al., 1980; Le Cloirec et al., 1983). Moreover, the use of carbon adsorption for the reduction of haloform precursors (Anderson et al., 1981) and trihalomethanes produced by chlorination process, has contributed to a comprehensive investigation of adsorption characteristics of natural organic compounds (McCreary and Snoeyink, 1981). Many recent works showed the influence of adsorption system characteristics, such as pH, salt type, salt concentration and ionic heterogeneity in multicomponent adsorption systems, on the removal efficiency of humic and fulvic substances by activated carbon (McCreary and Snoeyink, 1980; Randtke and Jepsen, 1982; Weber et al., 1983). The purpose of this study is to examine the effect of a main component of domestic detergents, sodium triphosphate (STP), on the adsorptive capacities of powdered activated carbon (PAC) for commercially supplied humic acids, at different pH values in distilled water. Also, the effect of STP concentration and pH on the adsorption affinity of the PAC for humic acids, is discussed in relation with electrokinetic properties of carbon particles (zeta potential measurements).A first batch equilibrium study (Figs 1 and 2), showed an effective enhancement of adsorption capacity for humic acids as a function of STP concentration, in a non buffered media (pH of distilled water, close to 5.0). For example, visible absorption analysis of humic acids indicates an increase of 93% (500 mg l⁻¹ PAC) and 133% (1000 mg l⁻¹ PAC) in the carbon adsorption efficiency for a STP concentration from 0.2 to 1.0mM. A second batch equilibrium study (Figs 3 and 4) led to adsorption isotherms for humic acids in distilled water, as a function of STP concentration and initial pH value of the non buffered multicomponent system. Freundlich isotherms showed an increase in the adsorption capacity of the PAC for humic acids, with a decrease in pH and an increase in STP concentration. However, the adsorption capacity for humic acids is quite reduced at high pH values in presence of STP, in comparison with results obtained with distilled water.Electrokinetic measurements on PAC suspensions (Fig. 5) indicates that both humic acids and STP induce a negative variation of the zeta potential of carbon particles. In such a binary system, the zeta potential is a linear function of the pH; the negative surface charge of the carbon increasing with an elevation of pH (Fig. 6). Therefore, it appears that some adsorption of triphosphate polyanion from solution could occur, contributing then to the apparent negative surface charge of PAC particles.It has been previously showed that the type of anion in sodium salts, had little effect on the enhancement of adsorptive capacities of activated carbon for humic substances (Lafrance and Mazet, 1985), due to Na⁺ ions. However, adsorption of TP anions on the carbon surface may produce a source of repulsive charges, unfavourable to the co-adsorption of humic acids as the pH of the binary system reach more basic conditions. The influence of possible electrostatic interactions between adsorbates at the carbon surface, on the adsorption efficiency for humic acids, could then be studied by zeta potential measurements of PAC particles during the adsorption process.     

Concentration, fractionation and characterisation of soluble organic phosphorus in river water entering lough neagh

The mean concentration of soluble organic phosphorus in the 6 major rivers entering Lough Neagh from 1975 to 1979 was 38 μg P 1⁻¹. Soluble organic phosphorus constituted 16% of the total phosphorus input during this period. The chemical nature and availability for algal growth of soluble organic phosphorus is largely unknown. An adsorption-precipitation technique for concentrating soluble organic phosphorus from 1001. volumes of river water was developed using lanthanum. From the lanthanum-phosphorus precipitate acid-soluble and alkali-soluble concentrated solutions of organic phosphorus were obtained. 25% of the soluble organic phosphorus from 6 river samples was acid-soluble and 40% was subsequently alkali-soluble. These concentrated solutions were subjected to gel filtration chromatography on a preparative scale using Sephadex G-50 and G-75 when soluble organic phosphorus compounds were fractionated by molecular weight. Of the acid-soluble organic phosphorus 40% was of mol. wt > 10,000, 20% was of mol. wt between 10,000 and 1500 and 40% was of mol. wt < 1500. When the alkali-soluble organic phosphorus was fractionated 70% was of mol, wt > 50,000. Although the acid-soluble concentrates were yellow in colour and may have contained fulvic acids, further gel filtration chromatography of the acid-soluble organic phosphorus with mol. wt > 10,000 indicated that the organic phosphorus was itself coloourless. Alkali-soluble concentrates were red-brown in colour and may have contained humic acids. Sufficient of the alkali-soluble organic phosphorus with mol. wt > 50,000 was isolated by precipitation on acidification for elemental analyses and infrared spectroscopy. Elemental analyses (45.9%, C, 6.6% H, 5.7% N, 0.6% P) showed that the composition of the precipitated material was not identical to the composition of soil humic acids being lower in carbon and higher in hydrogen, nitrogen and phosphorus. Infrared absorption spectra were, however, characteristic of humic substances. Phosphorus may be an integral part of the humic acid structure or an organic phosphorus-metal-organic matter complex may exist. Iron was present in the structure but the phosphorus to iron ratio was not constant between river samples. Algal bioassays on the acid-soluble organic phosphorus with mol. wt > 10,000 and the alkali-soluble organic phosphorus with mol. wt > 50,000 showed that 10 and 32% respectively were available for growth under the conditions of the test.     

An automated procedure for the determination of total Kjeldahl nitrogen

A procedure for the determination of total Kjeldahl nitrogen in surface fresh waters and organic wastes is described. Organic nitrogen compounds are converted to ammonium sulphate by a catalytic (red mercuric oxide) acid-sulphate digestion. The digest time is 3 h and allows for a maximum of 36 samples, 2 blanks and 2 standards to be processed simultaneously. There is no pH adjustment required following the digestion. Calibration curves covering the ranges (i) 0.5–100 μg NH₃---Nl⁻¹ and (ii) 10–1000 μg NH₃---Nl⁻¹ were linear within ±2%. The detection limit of the method is 0.5 μg TKNl⁻¹. The concentration range of TKN for which the method is suitable is 0.5 μg Nl⁻¹–40 mg Nl⁻¹. The method displayed a high tolerance to interferences from copper, iron, mercury and hardness. Digest procedure gave a high recovery and reproductibility over a wide range of nitrogen compounds tested.