Testing aluminum-chelate equilibria models using sorghum root growth as a bioassay for aluminum

Aluminum toxicity is an important limitation to crop yields in the acid soils of southeastern U. S. and other parts of the world due to its detrimental effects on roots. Soluble organics in soil solution ameliorate Al toxicity, a phenomenon which can be studied employing synthetic chelates. Theoretical models predict that Al will be complexed on nearly a one to one molar basis by nitrilotriacetic acid (NTA) at toxic pH levels found in acid soils (4.0 to 4.5). A series of growth chamber experiments were conducted with NTA at various Al and pH levels to test equilibrium models using sorghum [Sorghum bicolor (L.) Moench] as a bioassay for the uncomplexed Al. At pH 3.5 neither Al nor NTA affected root growth which was very poor, probably because of H⁺ toxicity. At pH 4.0 and 4.5 root growth was reduced by Al levels, and NTA ameliorated toxicity as predicted by the theoretical model. Root length was reduced at pH 4.0 relative to pH 4.5 indicating that H⁺ ion was toxic at pH 4.0. The bioassay method was successful in confirming the model for Al-chelate equilibria for NTA. Differential pulse polarography was found to be sensitive to the uncomplexed Al and may have potential in determining toxic Al in soil solution.     

Ecological and physiological responses of Atlantic salmon in acidic organic rivers of Nova Scotia,Canada

Ecological and toxicological data from field studies on acidic rivers of Nova Scotia were examined to review the effects of low pH on Atlantic salmon (Salmo salar) populations in waters rich in organic acids where noexchangeable forms of Al dominate at all times. There were no survival of salmon past the dry stage at pH <4.7, and survival rates for salmon from egg to smolt only increased at pH >4.9. Annual production of juvenile salmon and potential yield of smolts were lower at pH 4.7 to 5.4 than at pH 5.6 to 6.3 because of reduced densities attributable to the high mortality of fry at pH ≤5.0. However, acidity episodes to pH <4.7 also resulted in mortality of parr, reducing densities and often completely eliminating year-classes. The physiological responses of juvenile salmon to chronic acid conditions and to acute acidity typical of episodic events were also reviewed in relation to toxicity. Decreased in plasma Na and Cl were well correlated with ambient pH, but not with exchangeable Al concentrations in rivers. These plasma electrolytes provided reliable indicators of the thresholds for sublethal effects on ionoregulatory mechanisms. There was no morphological evidence of damage or lesions in gill epithelia, indicating that accumulation of Al in the gills of parr was not a significant factor in the lethal effects observed in acidic rivers. High organic matter content in the water apparently protected gills from adverse Al effects. Toxicity was considered to result from the effect of low ambient pH on branchial ionoregulatory mechanisms.     

Localization of aluminum in tissues of fish

The concentrations of Al in fish gills has been used as a measure of fish exposure to this metal in acidified waters. This experiment was designed to determine if other fish tissues also accumulate Al and thus possibly contribute to the cause of death. Rainbow trout (Salmo gairdneri) were exposed to the following fours test conditions for 48 hr or until death: (1) pH 6.8, <0.001 mg.L^?1 Al (n=6); (2) pH 5.2, <0.001 mg₁L^?1 Al (n=2);(3) pH 5.2,1.0 mg.L^?1 Al (n=5); (4) pH 6.8, 1.0 mg.L^?1 Al (n=3). The trout were held in synthetic, low Ca water prior to, and during, experimentation. Esophagus-stomach, gonad, gall bladder, gill (left and right), heart, intestine, kidney, liver, muscle (epaxial), and spleen were digested in a 4:1 mixture of HNO₃:HClO₄ and analyzed by Inductively Coupled Plasma Emission Spectrophotometry. Elevated Al concentrations were found in gill and gastrointestinal tissues. Left and right gills of fish exposed to pH 5.2, 1.0 mg.L^?1 Al were the only tissues found to be significantly different (p<0.01) between the test conditions. The mean total Al concentrations of these test 3 fish, for the left and right gill were 3.61 and 4.33 mg.g^?1 Al dw. The Al concentration in thle gastrointestinal tissues of the fish exposed to pH 6.8 at 1.0 mg.L^?1 Al was greater than that of the control fish, but not statistically significant. These results suggest that the analysis of whole gill remains an effective indicator of Al exposure in fishes at low pH.     

Acid stress and extinction of a spring-spawning fish population

Investigation of Heeney Lake, 21.7 ha, revealed a small population of white sucker, Catostomus commersoni. Only four age-classes were represented in this normally abundant and long-lived species. By 1984 only one new age-class had been recruited into the population. As these fish spawned in the outlet stream in early spring, the potential toxicity of these waters was assessed at two snow-melt events. Rainbow trout, Oncorhynchus mykiss, of hatchery origin were held in the outlet stream as pH declined from 6.5 to 4.7 during a snow melt, late February. Trout showed a loss of 19% in plasma Na and 24% in Cl concurrent with gill Al concentration increasing from 10 to 250 μg'g^?1 dry wt. At the mid-April snow melt, pH fell to 4.1, and rainbow trout held in the outlet showed a decline in plasma sodium of 42% and gill Al increased from 10 to 415 μg'g^?1 dry wt. Control rainbow trout held in Harp L. at pH 6.3 showed no significant change in plasma and muscle ion concentrations, or in gill Al concentration. White sucker from nearby waters were held in Heeney Lake outlet, late April, and muscle Na and Cl declined significantly as gill Al concentration increased from 11 to 50 μg'g^?1 dry wt during 48 hr exposure. White sucker hekl in Heeney L. outlet, mid-May, showed no significant change in plasma ions. No white sucker have been captured in Heeney L. since 1984 and the population is presumed to be extinct. Acid deposition has declined in recent years but lake and stream pH have not recovered and fish populations may still decline or disappear.     

The effects of low pH,low calcium concentrations and elevated aluminium concentrations on sodium fluxes in brown trout,Salmo Trutta L.

The effects of pH (c. 7.0, 5.4, 4.5 and 4.0), nominal Al levels (0 and 8 μmol L^?1) and Ca levels (10 and 50 μmol L^?1) on Na influx, efflux and netflux of brown trout have been investigated using artificial lake water of known composition. Low pH had little effect on influx, but tended to increase efflux, particularly in the low Ca treatments. A nominal addition of 8 μmol Al L^?1 at pH 4.5 and 4.0 reduced influx significantly. Efflux was unaffected. Aluminium addition at pH c. 7.0 and 5.4 had no such effect. The measured Al concentrations at the end of the static 8 hr flux measuring experiments were markedly lower than the nominal amount of A1 added to the start.     

施用碱稳定固体减轻酸性土壤的酸度和铝毒

A pot experiment was catried out to study alleviation of soil acidity and Al toxicity by applying analkaline-stabilised sewage sludge product (biosolids) to an acid clay sandy loam (pH 5.7) and a strongly acidsandy loam (pH 4.5). Barley (Hondeum vulgare L. cv. Forrester) was used as a test crop and was grownin the sewage sludge-amended (33.5 t sludge DM ha^-1) and unamended soils. The results showed that thealka1ine biosloids increased soil pH from 5.7 to 6.9 for the clay sandy loam and from 4.5 to 6.0 for the sandyloam. The sludge product decreased KCl-extractable Al from 0.1 to 0.0 cmol kg^-1 for the former soil and from 4.0 to 0.1 cmol kg^-1 for the latter soil. As a result, barley plants grew much better and grain yield increased greatly in the amended treatments compared with the unamended controls. These observations indicate that alkaline-stabilised biosolids can be used as a liming material for remedying Al phytotoxicity instrongly acid soils by increasing soil pH and lowering Al bioavailability.     

Aluminum status of synthetic Al–humic substance complexes and their influence on plant root growth

Abstract

Aluminum (Al)–humus complexes are abundant in the A horizons of non-allophanic Andosols and contribute to the unique properties of volcanic ash soils, such as high reactivity with phosphate ions and a low bulk density. Natural non-allophanic Andosols commonly show Al toxicity to plant roots. There have been very few studies examining the contribution of Al–humus complexes to the Al toxicity of plant roots, although the complexes are the probable source of the toxic Al. We extracted humic substances from the A horizon of a non-allophanic Andosol using NaOH solution and reacted the humic substances and partially neutralized the AlCl₃ solution at three pH conditions (pH 4.0, 4.5 and 5.5) to prepare pure Al–humic substance complexes. The Al solubility study (equilibrium study in 10^?2 mol L^?1 CaCl₂) and the Al release study (a stirred-flow method using 10^?3 mol L^?1 acetate buffer solution adjusted to pH 3.5) indicated that all the synthetic complexes easily and rapidly release monomeric Al into the liquid phase with slight changes in pH and ion strength, although the Al contents and their extent of polymerization are considerably different among the complexes. A plant growth test was conducted using a medium containing the Al–humic substance complexes and perlite mixture. Root growth in burdock (Arctium lappa) and barley (Hordeum vulgare L.) was reduced equally by all three complex media, and the roots showed the typical injury symptoms of Al toxicity. These results indicate that in soils dominated by Al–humus complexes the Al released from the Al–humus complexes, as well as the exchangeable Al adsorbed by soil minerals, is definitely toxic to plant roots.     

Screening clover and Lotus rhizobia for tolerance of acidity and aluminium

Clover rhizobia (55 strains) were screened for tolerance of acidity and Al, using the technique of Keyser and Munns (1979). Assessment of visible turbidity after 14 days indicated three strains tolerant of pH 4.5 (although growth rate was reduced), 25 strains tolerant of 5μm Al and no strains tolerant of 50 μ m Al at pH 5.5.50 μmAl caused a decrease in the numbers of acid-tolerant strains at pH 4.5. Tolerance of acidity or Al was not associated with the pH or Al status of the soil from which a strain was isolated.Screening of eight strains of clover rhizobia and nine strains of Lotus rhizobia using turbidity assessment and viable counts indicated seven strains of clover rhizobia with different degrees of tolerance of 20 μm Al but none tolerant of 50 μm Al at pH 5.5. All Lotus rhizobia (both slow- and fast-growers) were tolerant of 20 and 50 μm Al at pH 5.5, with 50 μm Al causing a reduction in growth rate.Subculturing of strains in non-stressed and stressed media had no effect on the response to 50 μmAl at pH 5.5.     

Water Quality Dependent Recovery from Aluminum Stress in Atlantic Salmon Smolt

In Norway, a variable pH target (pH 6.2–6.4 during most of the year, but 6.4 during the smoltification period) is used to reduce the cost of liming salmon rivers. Here we test the adequacy of this liming strategy. Atlantic salmon presmolts exposed to sublethal acidic water (pH 5.9, <25 µg Ali·L^?1) for more than 3 months showed impaired sewater tolerance, elevated gill-Al concentrations, severe gill tissue changes, elevated blood plasma glucose concentrations, but no effect on blood plasma chloride. It is usually assumed that smolt will recover from prior aluminum (Al) exposure if water quality is restored. Recovery rate is here used as an indirect measure of water quality improvements achieved after treating acid water (pH 5.8, 85 µg Ali·L^?1) with lime to reach pH-target levels of 6.0 – 6.3. Fish were exposed in a channel-tank set-up for >210 hrs in water aged from 1 minute up to 2 hours after treatment (in a flow through system). More Al was eliminated from the gills when the fish were exposed to pH 6.3 than to pH 5.8 or 6.0, and when water was aged after pH increase. Recovery, defined as return of normal gill morphology, blood homeostasis and establishment of seawater tolerance was achieved within 210 hrs in channels treated with lime to pH 6.3, while a similar recovery was not obvious at lower pH values. Liming to pH 6.3 detoxified Al better than pH 6.1.     

Impact of Simulated Acid Rain on Growth and Yield of Two Cultivars of Wheat

The present study reports the results of a field-basedexperiment conducted to assess the effect of simulated acid rain(SAR) of different pH i.e. 5.6 (control), 5.0, 4.5, 4.0 and 3.0on two cultivars of wheat (Triticum aestivum, Malviya 213(M213) and Sonalika). Shoot and root lengths significantlydeclined at pH 3.0 in both varieties. Leaf area declined at pH4.0 and 3.0 in M213 at both ages and at 75 days in Sonalika.Total biomass of 75 days plants declined significantly at pH range4.5–3.0 in M213 and at pH 4.0 and 3.0 in Sonalika. Netassimilation rate (NAR) declined significantly at pH 3.0 inboth varieties. Compared to control, yield of M213 showedsignificant reductions at pH 4.0 and 3.0, whereas Sonalikaresponded negatively at pH 3.0. The study showed that acid rainhas a significant negative effect on wheat plant performance.     

Aluminum and iron(III) species in the soil solution including organic complexes with citrate and humic substances

The solubility of Al and Fe in soil is of relevance for their toxicity and availability, respectively, to plant roots. Humic substances as the main part of stable soil organic matter and citrate which is often excreted by P deficient plants are strong complexants of Al and Fe(III). Therefore, equations were developed to calculate the Al and Fe(III) species distribution in the soil solution in the presence of humic substances and citrate as organic ligands. Calculations in the pH range 4.0–7.0 showed that at higher pH humic-Al complexes were the most important species whereas AlOH-citrate^? dominated between pH 4.0 and 5.4. Free monomeric Al and AlSO₄⁺ were of minor relevance. Iron(III) species calculations showed that humic-Fe complexes were the main species in the pH range 4.0–7.0. But if mugineic acid, a Fe complexing phytosiderophore released into the rhizosphere by graminaceous plant species, was present in the soil solution (10^?6 M), Fe-mugineic acid complexes accounted for most of the Fe in solution. Fe-citrate^? was relevant at lower pH but contributed little to Fe(III) species at pH > 6.0. The results demonstrate the strong importance of the considered organic ligands for Fe and Al in the soil solution.     

Characterization of Rhizobium trifolii isolated from soils of different pH

Rhizobium trifolii were isolated from soils along a transect covering a range of soil pH (3.6–5.6) using two varieties of white clover by either growing seedlings directly in soil or in nutrient solution in tubes inoculated with soil. Rhizobia were present at pH 4.5 but absent at pH 3.9. Neither nodule number nor effectiveness were influenced by the method of isolation and the clover variety on which the strain was isolated. There was no relationship between the pH of the soils and either the number of nodules or the effectiveness of the isolates from those soils. Screening the isolates for tolerance of acidity and Al showed that multiplication was unaffected at pH 5.0 but was slowed for all strains at pH 4.5. Multiplication at pH 5.5 was unaffected by 10 μM Al but was inhibited by 50 μM Al. At pH 4.5 all but 16% of the isolates were inhibited by 10 μM Al; none multiplied with 50 μM Al. The strains which multiplied at pH 4.5 with and without Al were isolated equally from soils in the range pH 4.5–5.6. They were also isolated in almost equal proportions from the two varieties of clover and by the two isolation methods. Overall there was little variation in the effectiveness and acid- and Al-tolerance of isolates from these soils of different pH.     

Aluminum toxicity in tomato. Part 2. leaf gas exchange,chlorophyll content,and invertase activity

The effect of aluminum (Al) toxicity on leaf gas exchange, leaf chlorophyll content, and sucrose metabolizing enzyme activity of two tomato cultivars (Lycopersicon esculentum Mill. ‘Mountain Pride’ and ‘Floramerica') was studied to determine the mechanism of growth reduction observed in a related study (Simon et al., 1994, Part 1). Plants were grown in diluted nutrient solution (pH 4.0) with 0, 10, 25, or 50 μM. Al for 16 days. Leaf gas exchange was reduced 2–3 fold in both cultivars as Al concentration increased. Gas exchange of ‘Mountain Pride’ was more sensitive to Al toxicity than ‘Floramerica’, agreeing with growth responses observed. Reductions in carbon dioxide (CO₂) assimilation rate appeared to be due to nonstomatal factors in ‘Floramerica’, but stomatal and non‐stomatal limitations in ‘Mountain Pride’. Chlorophyll content of leaves was not affected by Al. Acid invertase (AI) and neutral invertase (NI) activity of roots responded consistently to Al concentration in both cultivars. Root AI and NI activity decreased to a greater extent for ‘Mountain Pride’ than for ‘Floramerica’.     

Effects of phosphogypsum or calcium sulfate on aluminon reactive aluminum in solutions at varying pH

Abstract

Growing evidence of positive crop responses to gypsum or phosphogypsum (PG) application in acid soils strongly support the use of these amendments as an ameliorant of subsoil acidity. Although gypsum improves Ca availability in subsoils, its role in alleviation of Al toxicity needs careful attention. In the current study, either PG, CaSO₄.2H₂O or CaCl₂.2H₂O was added (to supply 12 mM Ca) to solutions containing 40 μM Al at pH 4.1 + 0.1. Solution pH was gradually raised to 4.5, 4.8 and then to 5.3 at various time intervals during 25 d aging of the solutions at 25 + 1^OC.

Concentration of Al measured by aluminon method without preacidification and preheating, referred to as “reactive Al”; in this paper, was 16 μM in 2 g L^‐1PG solution without added Al. This accounted 38% of total soluble Al in PG solution. Addition of 2 g L^‐1PG to solution containing 40 μM Al, resulted in only 42% of total Al in solution present in forms reactive with aluminon. According to MINTEQ speciation model, Al in solution was present as an entirely complexed form with F^‐. An increase in solution pH up to 5.3 had no effect on measured concentration of reactive Al or predicted distribution of Al species.

Addition of CaSO₄.2H₂O to 40 μMAl solutions had no effect on the concentration of reactive Al within pH 4.1 ‐4.8, however, up to 62% of total Al was in a form complexed with SO₄ ^2‐, as predicted by MINTEQ model. The concentration of reactive Al decreased by 60% at pH 5.3. Addition of CaCl₂.2H₂O also had no effect on the concentration of reactive Al within pH 4.1 ‐ 4.8. Nearly 73 ‐ 94% of total Al was present in Al³⁺form. An increase in pH to 5.3, decreased the concentration of reactive Al by 27%. The results suggest that ion‐pairing of Al with F^‐would appear to be a possible mechanism for alleviation of Al toxicity by PG at pH range 4.1 ‐ 5.3. With regard to CaSO₄.2H₂O, at pH 4.1 ‐ 4.8 ion‐pairing with SO.₄ ^2‐appears to be possible mechanism for the alleviation of Al toxicity. In addition, at pH 5.3 a considerable decrease in reactive Al was evident which would further alleviate Al toxicity.     

Supernatant solutions containing various levels of aluminum and similar concentrations of phosphorus for aluminum phytotoxicity studies

Abstract

Precipitation of Al(OH)₃ and aluminum phosphate may occur in nutrient solution if a large amount of Al and P have been added to a relatively high pH. The objective of this study was to develop and test a supernatant‐solution method for Al phytotoxicity studies with large and/or old plant seedlings. Effects of pH and additions of Al and P on ionic strength and concentrations of Al and P in supernatant nutrient solutions were investigated. Two sets of supernatant nutrient solutions at two pH levels were prepared. The pH 4.0 set and 4.5 set contained seven levels of Al (maximum Al concentration of 6355 and 378 μM) and similar P concentration about 32 and 6 μM P, respectively. The Al concentrations in supernatant solutions were dependent on preparation procedure. The pH 4.0 set was tested in the greenhouse study with 6‐month‐old citrus seedlings and found to be successful as culture solutions for Al phytotoxicity studies. These two sets are suitable for growth of large (about 0.3 m) and/or old (about 6 mon.) seedlings. This supernatant‐solution method makes it possible to study Al phytotoxicity of large and/or old seedlings, to avoid the confounding effects of P on Al with respect to plant growth, and to report the actual concentrations of Al and P in growth solutions.     

Alleviation of Soil Acidity and Aluminium Phytotoxicity in Acid Soils by Using Alkaline-Stabilised Biosolids

A pot experiment was carried out to study alleviation of soil acidity and Al toxicity by applying an alkaline-stabilised sewage sludge product (biosolids) to an acid clay sandy loam (pH 5.7) and a strongly acid sandy loam (pH 4.5). Barley (Hordeum vulgare L. cv. Forrester) was used as a test crop and was grown in the sewage sludge-amended (33.5 t sludge DM ha-1) and unamended soils. The results showed that the alkaline biosloids increased soil pH from 5.7 to 6.9 for the clay sandy loam and from 4.5 to 6.0 for the sandy loam. The sludge product decreased KCl-extractable Al from 0.1 to 0.0 cmol kg-1 for the former soil and from 4.0 to 0.1 cmol kg-1 for the latter soil. As a result, barley plants grew much better and grain yield increased greatly in the amended treatments compared with the unamended controls. These observations indicate that alkaline-stabilised biosolids can be used as a liming material for remedying Al phytotoxicity in strongly acid soils by increasing soil pH and lowering Al bioavailability.     

The influence of ph on aluminium toxicity in the phytoplankton species Monoraphidium dybowskii and M. griffithii

The toxicity of aluminum on the phytoplankton species Monoraphidium griffithii and M.dybowskii (Chlorophyceae) was investigated. At pH 6.8 and low humus concentration, the growth of both species was reduced at 100–200 μg Al/l, whereas at pH 4.8 only the growth of M.griffithii was affected. The toxicity on the two species showed different relations to the pH-value. The results, supported by analyses of Al-fractions — total acid soluble, total monomeric and none-labile monomeric Al — indicate that the Al-toxicity is species-dependent, and that aluminium, soluble at neutral pH-conditions, can be toxic to the phytoplankton.     

Stabilization of dissolved organic matter by aluminium: a toxic effect or stabilization through precipitation?

Carbon mineralization in acidic forest soils can be retarded by large concentrations of aluminium (Al). However, it is still unclear whether Al reduces C mineralization by direct toxicity to microorganisms or by decreased bioavailability of organic matter (OM) because dissolved organic matter (DOM) is precipitated by Al. We conducted an incubation experiment (6 weeks) with two DOM solutions (40 mg C litre^?1) derived from two acidic forests and possessing large differences in composition. Aluminium was added to the solutions in realistic ranges for acidic soils (1.6–24 mg Al litre^?1) at pHs of 3.8 and 4.5, to achieve differences in Al speciation. We determined different Al species, including the potentially toxic Al³⁺, by Diffusive Gradients in Thin Films (DGT) to evaluate toxic effects on microorganisms. Precipitation of OM increased with larger amounts of added Al and higher pH, and we measured a larger fraction of dissolved ‘free’ Al at pH 3.8 than at pH 4.5. Organic matter degradation decreased significantly with Al addition, and we found more organic matter degraded at pH 3.8 than at pH 4.5 for the respective Al additions. Consequently, the observed reduction in OM degradation (i.e. stabilization) cannot be explained by toxic effects of ‘free’ Al. However, C stabilization correlated significantly with C precipitation. The pH did not influence C stabilization directly, but determined the amount of C being precipitated. Phosphorus was removed along with OM by precipitation, which possibly also affected C stabilization. We conclude that C stabilization upon Al addition did not result from toxic effects, but was caused by reduced bioavailability of OM after its precipitation. The reduction in OM degradation by 65% is of great relevance for the overall C stabilization in acidic forest soils. Increasing pH and decreasing Al concentrations upon recovery from acidic deposition should therefore not result in decreased stabilization of precipitated OM.     

Hydroponic Study of Aluminum Accumulation by Aquatic Plants: Effects of Fluoride and pH

The potential of five common aquatic plant species (Typha latifolia, Myriophyllum exalbescens, Potamogeton epihydrus, Sparganium angustifolium and Sparganium multipedunculatum)to be used for Al phytoremediation was tested. The plants were exposed, for 14 days under hydroponic conditions, to synthetic effluents representing extreme conditions that could occur accidentally at an aluminum refinery site. Tested Al concentrationsranged between 0 and 400 μM, fluoride concentrations between 0 and 900 μM, and the pH varied from 4.5 to 7.5. The results indicate that all the plants tested accumulated aluminum, and as a result induced a decrease of Al in the ambient water. For individual species Al uptake (in mol g^-1 dw d^-1) decreased in the following order: Myriophyllum exalbescens > Sparganium sp. ≌Typha latifolia > Potamogeton epihydrus. M. exalbescens accumulated Al more rapidly in its leaves than in other tissues, whereas T. latifolia and Sparganium sp. accumulated Al essentially in their roots. For P. epihydrus the relative importance of the leaves and roots varied with exposure conditions. For all species, fluoro-Al complexes contributed to Al uptake, contrary to the predictions of the Free-Ion Model, according to which the bioavailability of aluminum should be best predicted by the concentration of the free ion, Al³⁺. The influence of pH on Al uptake varied among the different species and among the parts of the plant: competition between Al and the H⁺-ion was evident for the roots of T. latifolia and the leaves and stem of M. exalbescensand P. epihydrus, whereas the roots of M. exalbescens, P. epihydrus and Sparganium sp. showed an inverse trend (Al uptake increased at low pH). For the leaves of T. latifolia and Sparganium sp., no pH influence could be demonstrated. Overall, the results of this study indicate that aquatic plants have a potential for Al phytoremediation.     

Determination of Toxicity of Spoil Substrates After Brown Coal Mining Using a Laboratory Reproduction Test with Enchytraeus crypticus (Oligochaeta)

Laboratory-reared cultures of Enchytraeus crypticus were used in a reproduction toxicity test to evaluate the toxicity of 46 spoil substrates collected in four brown coal mining areas in the Czech Republic and Germany. A set of substrate parameters (pH, conductivity, Na, Ca, K, Al, Fe, loss of ignition and polyphenol contents) were measured for each spoil and correlated with spoil toxicity for E. crypticus. Toxicity increased with decreasing pH and increasing Al, Fe content. Spoil with a pH below 3 did not support the survival of E. crypticus. However, some alkaline spoils with high conductivity and ion concentration were also toxic. Toxicity was positively correlated with the loss of ignition and polyphenol content. The results indicate that the toxicity of post-mining spoil substrates have multiple origins. Most frequently the toxicity of post-mining substrates corresponds with low pH and consequent toxicity of Al and Fe. However some substrates may be toxic due to high ion concentrations. The potential role of fossil organic matter (namely polyphenols) in toxicity of post-mining substrates requires further research.