Changes In Heavy Metal Contents Research Articles

Methods for controlling heavy metals in environmental soils based on artificial neural networks

The problem of heavy metal pollution in soil has become a global environmental problem, and it is very important to predict and manage the heavy metals in the environmental soil in a timely manner. The changes in heavy metal content in soil have characteristics such as nonlinearity and large delay, making it difficult to predict heavy metals in soil using traditional methods. Traditional prediction methods are complex and cumbersome, which can lead to longer treatment time and easy secondary pollution. This article analyzed the Back Propagation neural network (BPNN) in artificial neural networks (ANN) and applied it to the prediction of heavy metals in environmental soils. BPNN has good nonlinear function approximation ability, so it can be well applied to complex problems such as soil heavy metal prediction. The methods of treating soil heavy metals include physical repair method, chemical repair method, microbial repair method, plant repair method, plant microbial combined repair method and so on. The use of BPNN can predict heavy metals in environmental soils through adaptive dynamic learning. However, the training time of the BPNN is relatively long and the convergence speed is relatively slow. Therefore, additional momentum terms were added to adjust the weights and thresholds of the network to improve the BPNN. In the experiment, the prediction performance of the improved BPNN was compared before and after the improvement. This article took 50 monitoring data of heavy metals in the same soil in a certain region in 2021 as sample data and predicted the content of heavy metals in the soil using improved and improved BPNN. Due to time constraints, this article only conducted experimental analysis on heavy metals such as lead and cadmium. In the first experiment, when the soil sample data was 50, the prediction accuracy of the BPNN for cadmium before and after improvement was 75.95% and 89.56%, respectively. In the second experiment, when the soil sample data was 50, the prediction accuracy of the BPNN for cadmium before and after improvement was 77.99% and 89.85%, respectively. The improved BPNN has good prediction accuracy and can effectively predict the status of heavy metals in soil. The analysis in this article can provide scientific basis for the comprehensive prevention and control of heavy metals in regional soil, and also provide reference for the development of pollution-free agriculture and ensuring food safety.

Potential of Intercropping Pennisetum purpureum Schum with Melia azedarach L. and Broussonetia papyrifera for Phytoremediation of Heavy-metal Contaminated Soil around Mining Areas

In order to study the potential of intercropping Pennisetum purpureum Schum with Melia azedarach L. and Broussonetia papyrifera for phytoremediation of heavy-metal contaminated soil around mining areas, a pot experiment was conducted to investigate the effects of intercropping on plant biomass, heavy metal accumulation, dynamic changes in heavy metal content in soil solution, and response characteristics of the rhizosphere microbial community. The results indicated that the shoot biomass of P. purpureum and M. azedarach from their intercropping system (KX) was increased by 26.5% and 13.2%, respectively, and the shoot biomass of B. papyrifera from the intercropping system of P. purpureum and B. papyrifera (GX) was increased by 13.5% compared with their corresponding monoculture systems. The shoot Cd content of M. azedarach in the KX treatment was significantly increased by 24.9% (P<0.05), and their Cd and Pb accumulation in shoots were also significantly increased. The shoot contents and accumulations of Cd and Pb from P. purpureum in the GX treatment were significantly increased; however, those in B. papyrifera shoots were decreased. The total accumulations of Cd and Pb in each pot from intercropping systems were higher than that from the monoculture treatment, with that from the KX treatment being the highest at 1065 μg·pot-1. During the 150-day cultivation process, the pH value and dissolved organic carbon (DOC) content in the soil solution under the intercropping systems of KX and GX were higher than those of original soil (CK). After 150 d cultivation, the DOC contents of the soil solution under the KX and GX treatments were significantly increased by 40.5% and 33.1% in comparison with that under CK (P<0.05), respectively. Compared with those from CK and P. purpureum and B. papyrifera monoculture treatments, the Cd content in soil solution from the KX treatment was significantly decreased by 56.1%, 35.5%, and 46.5%, and that in the GX treatment was decreased by 54.5%, 33.2%, and 44.6% (P<0.05), respectively. The Shannon and Chao1 indices of rhizosphere microorganisms under the intercropping systems were significantly higher than those under CK. The number of unique OTUs in intercropping systems was significantly higher than that in CK and the M. azedarach and B. papyrifera monocultures. Intercropping improved the abundance of dominant bacteria such as Actinobacteriota and Acidobacteriota, and the abundance of Actinobacteriota increased by 31.6%, 20.9%, and 25.3% in the KX treatment and by 32.3%, 21.5%, and 25.9% in the GX treatment, respectively, in comparison with those in CK and the P. purpureum and M. azedarach monocultures. It was concluded that intercropping P. purpureum with wood plants could increase their shoot biomass and the accumulations of Cd and Pb, as well as soil environmental quality, whereas the availability and migration risk of heavy metals in soil were reduced. Moreover, the intercropping of P. purpureum and M. azedarach was more beneficial to the remediation of polymetallic-contaminated soil around mining areas.

Comparative assessment of biosorption potential of non-treated and acid-treated activated carbon produced from maize cob for wastewater treatment

Humans and the environment are both concerned about contaminated drinking water. One of the most dangerous constituents in wastewater is heavy metals. The removal of these contaminants from the ecosystem is still a challenge. Some of these heavy metals have been toxic concentrations in human and livestock drinking water. As a result, the goal of this study was to compare the adsorption potential of non-treated and acid-treated activated carbon generated from maize cob in the treatment of wastewater. Fresh maize cobs were air-dried and oven-dried at 255 °C for 9 hours after being cleaned in distilled water. These were crushed, sieved through a 300 μm mesh and carbonized in a muffle furnace to produce powdered activated carbon (PAC). One half of PAC was treated with 780 mL of hydrochloric acid (acid-treated activated carbon - AAC), while the other received no further treatment (non-treated activated carbon - NAC). For surface characteristics and functional groups, the conventional approach was applied to characterize AAC and NAC. Thirty grams of each sample were used in the treatment of metal recycling effluent. Untreated (T1), filtered (T2), NAC treated (T3), and AAC treated (T4) wastewater samples were analysed in three replicates using World Health Organization (WHO) and Lagos State Environmental Protection Agency (LASEPA) standard methods for Physico-chemical parameters. Analysis of data was by ANOVA, while mean separation was by Duncan’s Multiple Range Test (DMRT) at (P ≤ .05). Results showed that T2 had no significant improvement (P ≤ .05) in all parameters tested. T3 significantly increased pH, conductivity, TS and TSS, gave the highest mean alkalinity, but showed no significant changes in heavy metal contents. T4 significantly improved mean colour, conductivity, nitrate content and DO, reduced mean pH (from 7.4±0 to 2.1±0.1), increased heavy metal concentrations (P ≤ .05) and increased mean total acidity, but not significantly (P ≥ .05). Treatments improved parameters in the following order: filtration &lt; NAC &lt; AAC. Thus, acid-activated carbon had a higher adsorbent capability than non-activated carbon due to its wide surface area and low moisture and ash contents.

Soil Heavy Metal Content and Enzyme Activity in Uncaria rhynchophylla-Producing Areas under Different Land Use Patterns.

In this study, we investigated the content of soil heavy metals, the level of heavy metal pollution and the characteristics of soil enzyme activity under three different land use patterns of Uncaria rhynchophylla base, forestland and wasteland in Jianhe County, Qiandongnan Prefecture, Guizhou Province, revealing the intrinsic correlation between heavy metal content and soil enzyme activity to reveal the relationship between soil enzyme activity and heavy metal content under different land use patterns in the Uncaria rhynchophylla production area. The results showed that soil Cd and Hg contents in Uncaria rhynchophylla base both exceeded the national soil background value. The single pollution index indicated that Cd had the greatest contribution to Pn, and the comprehensive pollution index (Pn) demonstrated no heavy metal pollution in the soil of Uncaria rhynchophylla-producing areas. Under different land use patterns, the enzyme activity was forestland > wasteland > Uncaria rhynchophylla base, and catalase and acid phosphatase activities presented significant spatial differences (p < 0.05). The correlation between soil enzyme activity and heavy metal content was uncertain due to the changes in land use patterns and heavy metal species. The proportions of positive correlation and negative correlation between soil enzyme activity and heavy metals in Uncaria rhynchophylla base were 50%, respectively. In the forestland, soil enzyme activity was positively correlated with heavy metals, while in the wasteland, soil enzyme activity was negatively correlated with heavy metals. This study revealed that the changes in heavy metal content should be focused on for the soil quality in Uncaria rhynchophylla-producing areas under different land use patterns. The results of the study provide some basic theoretical references for the improvement of soil quality in the production area of Uncaria rhynchophylla under different land use practices.

Remediation Potential of Three Dwarf Bamboos on Farmland Soils Contaminated with Mixed Heavy Metals

A two-year field experiment was carried out in a Cu-Zn-Cd-Pb-contaminated field with Sasa auricoma, Indocalamus tessellatus, and Shibataea chinensis Nakai to investigate their growth and accumulation characteristics. Based on changes in heavy metal content in the soil, we compared their phytoremediation potentials for the combined pollution of heavy metals. After two years of planting, S. auricoma showed the best tolerance to soil contaminated by heavy metals, with the number of plants being 63.8 times that at the time of planting. For each bamboo type, heavy metals were most concentrated in the root, with the best enrichment ability of Cd and worst ability of Pb. The bioconcentration factor of Cd in the roots was far greater than 1 for all three species, with 17.68 for S. auricoma and 14.63 for I. tessellatus. The accumulation of heavy metals was mainly concentrated in the roots and rhizomes, and the accumulations of Cu, Zn, and Cd in S. auricoma were 157.14, 363.3, and 7.18 g·hm-2, respectively, which were higher than those of I. tessellatus and S. chinensis Nakai. Compared with that before planting, the content of heavy metals in the non-rhizosphere soil decreased after two years of planting, among which Cd content decreased the most, from 39.6%-40.4%. In addition, the contents of Cu, Zn, and Cd in rhizosphere soil of S. auricoma and S. chinensis Nakai were significantly lower than those in non-rhizosphere soil (P<0.05). The results showed that the three species had strong accumulation ability of Cd and could be further studied as Cd-repaired plants. The growth condition and content and accumulation of heavy metals in S. auricoma were excellent among the dwarf bamboos, which showed the highest phytoremediation potential.

Changes in Heavy Metal Content of Blast Furnace Slag Cement According to Blast Furnace Slag Content

Changes in Heavy Metal Content of Blast Furnace Slag Cement According to Blast Furnace Slag Content

Processing and Storage Effects on the Proximate Composition, Changes in Heavy Metal Contents and Total Volatile Base Nitrogen (TVB-N) of Selected Fish Species in Osun State, Nigeria

This study assessed the effect of location, processing methods and storage on the proximate composition, heavy metal contents and total volatile base nitrogen (TVB-N) of some selected fish species from Asejire and Opa reservoirs, Osun state. The fish species were processed by salting, drying, smoking, storing (25 ± 2°C) and analyzed for proximate composition, heavy metal contents and TVB-N. Protein, fat, ash and carbohydrate increased after processing but moisture content reduced. During storage the heavy metal concentrations reduced but moisture content and TVB-N increased; indicators of deterioration. The study concluded that processes such as smoking, drying and salting contributed to the keeping quality of the fishes and reduced the bio-accumulated heavy metal concentrations of the fish species.

Application rate and plant species affect the ecological safety of sewage sludge as a landscape soil amendment

Recycling sludge as a soil amendment has become a viable option for sludge disposal. However, such application can lead to soil pollution because of its enrichment in contaminants, especially heavy metals. To identify an effective means to ensure the ecological safety of sewage sludge landscape utilization, a glasshouse experiment was conducted by mixing sewage sludge at 0%, 15%, 30%, 60%, and 100% (V/V) amendment ratios to landscape soils and planting five common landscape plants (Aphelandra ruellia, Syngonium podophyllum, Schefflera odorata, Alocasia macrorrhiza, and Dianella ensifolia). Sludge amendment significantly improved fertility and moisture retention capacity of soil, but dramatically increased the contents of Cd, Pb, Cu, and Zn. Compared with lateritic red soil (CK), sludge amended-soils increased the relative growth rate of landscape plants and enhanced their nutrient uptake and heavy metals accumulation. A rate of 30% or less of sludge application showed positive growth effects for all five landscape plants, and did not cause potential ecological risks of heavy metals to landscape soils. However, rates of 60% or higher posed very high potential ecological risk in multiple metals, particularly in Cd. Interestingly, S. odorata, A. ruellia and A. macrorrhiza could alleviate the ecological risks of Cd, Cu and Zn, respectively, and these results were confirmed by data of relative changes in heavy metal contents in post-experiment soil. Our results suggest that attention to reducing the environmental risks of heavy metals in sludge utilization as landscape soil-amendments should not only be paid to controlling the application dosage of sludge but also to planting suitable plant species.

Changes in heavy metal contents in animal feeds and manures in an intensive animal production region of China

The 360 feed and manure samples were collected from 150 animal farms in Jiangsu Province, China and analyzed for heavy metals. Concentrations of Zn and Cu in animal feeds were 15.9–2041.8 and undetected–392.1 mg/kg respectively, while Hg, As, Pb, Cd, and Cr in all feeds were below 10 mg/kg. Concentrations of Cu, Zn, and Cr in animal manures were 8.4–1726, 39.5–11379, and 1.0–1602 mg/kg respectively, while As, Cd, Hg, and Pb were < 10 mg/kg. The concentration of Cu, Zn, As and Cr in animal feed and manure were positively correlated (p < 0.001), but the Cd, Hg, and Pb were not statistically correlated between the feed and the manure. Concentrations of Cu and Zn were highest in pig feed and manure, followed by poultry and dairy feeds and manures. During 1990–2008, Cu, Zn, As, Cr, Cd contents increased by 771%, 410%, 420%, 220%, and 63% in pig manure, 212%, 95%, 200%, 791%, and −63% in dairy manure, and 181%, 197%, 1500%, 261, and 196% in poultry manure. Most of the increases occurred from 2002 to 2008, which reflects the extensive use of feed additives after 2002. In contrast, Pb and Hg in manures continuously decreased from 1990 to 2008. The results suggest that the heavy metal contents in animal manure have been greatly increased over 18 years and the contribution of manures to soil should be considered.

Changes in Heavy Metal Contents of a Waste Engine Oil Polluted Soil Exposed to Soil pH Adjustments

ABSTRACT The present study investigated the role of soil pH adjustments in heavy metalsconcentrations in waste engine oil (W EO) - polluted soils. Sun-dried top soil (0-10cm) wasmeasured into buckets. WEO was added to soil and mixed thoroughly to obtain similarconcentrations of 2.5% w/w oil in soil. The polluted soil was thereafter amended with NPK(15:15:15) fertilizer to enhance microbial activity. The buckets were transferred into a wellventilated screen house with inherent constant room temperature (27oC). The entire setupwas divided into 5 sets. Each set was wetted daily with 200ml of different pH solutions (pH3, 5, 7, 9, and 11) for a period of 3 months. There were significant reductions in heavymetal concentrations particularly at pH of 5. There were significant reductions in totalhydrocarbons contents (THC) of polluted soils at 2 months after pollution from 1882.32mg/kg at pH 3 to 325 mg/kg at pH 5, compared to THC of soil at 1 week after pollution atpH 7 (3425.63mg/kg).Keywords: Contamination factor; environmental risk factor; hazard quotient; naturalattenuation; pH; soil; waste engine oil.Research Article

Heavy Metal Transport and Behavior in the Lower Columbia river, USA

The primary objective of this study was to evaluate temporal changes in heavy metal content of lower Columbia River sediment following terminated or reduced soluble heavy metal loading from the world's largest lead-zinc refinery and mining districts in the USA and Canada. Sediment cores were collected from two fine sediment depositional sites ( approximately 600 km downstream) in August 1999 and were analyzed for total metal content, texture, and age/dating parameters. Zinc, cadmium and lead contents in 1999 declined by only a factor of two over their depth profile maxima (dated as between 1970 and 1980). In sharp contrast, more than a 10-fold decrease in dissolved metal loading occurred during this same period. Zinc in filtered Columbia River water at downstream locations also declined by > 10-fold, consistent with the reduced upper river solute-metal loading. Once soluble metal releases are reduced or terminated, the solute half-time in Columbia River water is months versus approximately 20 yr for adsorbed metals on surficial (or resuspended) bed sediments. The much slower rate of decline for sediment, as compared to the solute phase, is attributed to resuspension, transport and redeposition of irreversibly bound metals from upstream sedimentary deposits. This implies downstream exposure of benthic or particle-ingesting biota can continue for years following source remediation and/or termination of soluble metal releases. Accordingly, contaminant contents of both particulate and solute phases of river water, as well as sediment core sections, are suggested for assessing long-term biotic exposure/response to mitigation activities in the Columbia River and similar fluvial ecosystems.

Distribution and changes in heavy metal contents of paddy soils in different physiographic units of Bangladesh

The distribution and changes in the background levels of V, Cr, Mo, Ni, Cu, Zn, Pb, U, and As were assessed using 66 archived surface (Ap horizon) soil samples (22 for 1967 and 44 for 1995) analyzed by RIX 2000 x-ray fluorescence spectrometry to determine whether a soil was polluted or not during the period 1967–1995 in Bangladesh. Distribution of the mean V content showed lower values (<15.6 mg kg−1) in the soils of the Old Himalayan Piedmont Plain (OHP), Barind Tract (BT), and Madhupur Tract (MT), values ranging between 115.6 and 169.0 mg kg−1 (mean ± SD / 2) in the Tista Floodplain (TF), Brahmaputra Floodplain (BF), Meghna River and Estuarine Floodplain (MF), Northern and Eastern Piedmont Plains (NEP), and Chittagong Coastal Plain (CCP), and higher values (>169.0 mg kg−1) in the Ganges Floodplain (GF) and Surma-Kushiyara Floodplain (SKF). The mean Cr contents were lower (<84.7 mg kg−1) in OHP, TF, BT, and MT, ranged between 84.7 and 107.1 mg kg−1 in GF, BF, MF, NEP, and CCP, and a higher content (>107.1 mg kg−1) was recorded in SKF. The mean Mo contents ranged between 2.01 and 2.11 mg kg−1 in all the physiographic units except for a lower content (<2.01 mg kg−1) in TF and a higher content (>2.11 mg kg−1) in the MT unit. The mean Ni contents were lower (<39.5 mg kg−1) in OHP, TF, and BT, ranged between 39.5 and 62.3 mg kg−1 in GF, BF, MF, MT, NEP, and CCP and a higher content (>62.3 mg kg−1) was recorded in SKF. The mean Cu contents were lower (<23.4 mg kg−1) in OHP, TF, BT, MT, and NEP, ranged between 23.4 and 39.8 mg kg−1 in MF, SKF, and CCP, and a higher content (>39.8 mg kg−1) was recorded in GF and BF. The mean Zn contents were lower (<60.3 mg kg−1) in OHP, BT, MT, and NEP, ranged between 60.3 and 90.9 mg kg−1 in TF, MF, and CCP, and a higher content (>90.9 mg kg−1) was recorded in GF, BF, and SKF. The mean Pb contents were lower (<21.7 mg kg−1) in TF, BT, and NEP, and ranged between 21.7 and 25.3 mg kg−1 in the other physiographic units. The mean U content was lower (<3.47 mg kg−1) in NEP and an almost uniform distribution between 3.47 and 5.29 mg kg−1 was observed in the other physiographic units except for a higher content (>5.29 mg kg−1) in TF. The mean As contents were lower (<6.2 mg kg−1) in OHP, TF, and BT, ranged between 6.2 to 8.7 mg kg−1 in BF, MT, MF, NEP, and CCP, and a higher content (>8.7 mg kg−1) was recorded in the GF and SKF soils. The contents of V, Cr, Mo, Ni, Cu, Zn, Pb, V, and As in the peat soil were 222.2, 111.1, 2.11, 63.4, 57.4, 108.8, 25.4, 5.28, and 12.3 mg kg−1, respectively. However, the distribution of the V, Cr, Mo, Ni, Cu, Zn, Pb, V, and As contents was in the range of 43.3–275.0, 61.0–176.0, 1.90–2.21, 14.0–134.0, 8.7–65.7, 27.8–138.0, 14.3–31.0, 2.23–5.93, and 3.9–14.0 mg kg−1, with mean values of 142.3, 95.9, 2.06, 51.0, 31.6, 75.6, 23.5, 4.38, and 7.5 mg kg−1, respectively, in 1995. The heavy metal contents of the surface soils were, generally, higher on the lower slopes than in the middle or upper parts of the landscapes. A wide variation in the changes of heavy metal contents was observed among the soils of different physiographic units in Bangladesh. Changes in the V, Cr, Mo, Ni, Cu, Zn, Pb, V, and As contents showed higher increases up to 33.1, 25.0, 15.38, 28.5, 35.5, 24.9, 19.0, 22.10, and 34.6% and higher decreases down to 24.3, 13.1, 2.56, 36.4, 51.0, 21.5, 12.3, 18.98, and 40.0% respectively, with mean values remaining almost unchanged (−1.87 to +6.81%) except for a decrease of 17.1% Cu during the period 1967–1995. Results of this study suggested that the soil properties (clay, total Fe and Al contents, ECEC, total C content, pH, total Sand P contents) are important factors regulating the natural background levels of heavy metals in the soils of Bangladesh.

Changes in heavy metal contents in an acidic forest soil affected by depletion of soil organic matter within the time span 1969–93

Measurements of heavy metal content (Pb, Cd, Zn) were made in the period 1969–93 in a forested ecosystem near Möhlin (north-western part of Switzerland). Some distinct changes were found in the soil, especially in the subsoil (30–35 cm). The main and most likely driving force of the induced changes in the subsoil can be traced back to the observed decomposition of organic matter which strongly influenced the behaviour of major and minor chemical constituents of the soil. These changes are presumably mostly due to incidents that occurred in the past caused by the nearby aluminium industry. Generally, the observed changes in soil chemistry increase with decreasing distance to the aluminium plant in the time span 1969–93. The influence, if any, of the vegetation type and the forest management on the changes in the subsoil could not be figured out. Changes in the Pb content primarily correlate with soil organic matter (with a significant decrease in the subsoil). Good correlations are also found with Fe and partially with Al and Mn. Cd correlates well with pH, (earth)alkali ions, and generally to a lower degree with Mn, Fe and Al, but almost no correlation was found with the organic matter of the soil. Zn holds an intermediate position: significant correlations with organic C, (earth)alkali ions, Fe, Al and Mn were found but pH correlated only very weakly. The main transportation mechanism of Pb in the subsoil is believed to be primarily in colloidal form. Colloid release mechanisms are hypothesised to be due to the humus disintegration and the consequent reaction chain. In contrast to Pb, the elements Cd and Zn have, presumably, been translocated to a great extent as aqueous species.

Seasonal changes of cadmium and copper levels in stem-boring larvae of Agapanthia villosoviridescens (Coleoptera) on salt marshes of the Westerschelde Estuary.

Analyses of heavy metals in insects, including their developmental stages, have been widely used to monitor the penetration of these pollutants in various ecosystems. There are few reports dealing with seasonal changes in heavy metal content of insects. The seasonal pattern found in one herbivorous insect closely followed seasonal trends in metal contamination levels in the local vegetation. No data are available on season changes in insect larvae. To obtain more detailed information on seasonal changes of heavy metal levels in insects and their relation with the seasonally changing conditions in the habitat, the authors studied the time course of cadmium and copper concentrations in larvae of the longhorn beetle Agapanthia villosoviridescens. These live as stem-borers in the salt marsh halophyte Aster tripolium. The authors collected larvae from three salt marshes along the Westerschelde estuary. This estuary is severely polluted by heavy metals originating mainly from upstream sources; a large fraction of these metals is retained within the estuary. The fringing salt marsh soils, which are a sink for trace metals, show a gradient in pollution, with levels of heavy metals generally increasing in upstream direction. Salt marsh halophytes growing on these marshes show uptake of metals from the soil.more » Further transfers of heavy metals through the natural food chains on these salt marshes have not been investigated sofar.« less

Macophyte cycling of zinc, copper, lead and cadmium in the littoral zone of a polluted and a non-polluted lake. II. Seasonal changes in heavy metal content of above-ground biomass and decomposing leaves of Phragmites australis (Cav.) Trin.

The seasonal changes in heavy metal content of the above-ground biomass and decomposing leaves of Phragmites australis (Cav.) Trin. from the littoral zone of the eutrophic, sewage-polluted Lake Sortesø and the oligotrophic, non-polluted Lake Hampen, were investigated. It was found that the concentration of Zn in the leaves and stems and of Cu in stems is at a maximum during the growth season and decreases thereafter. The concentration of Cu in the leaves was more or less constant during the study period. The concentration of Pb in the leaves increased during and after the growth season, possibly as a result of atmospheric deposition. In decomposition experiments it was found that leaves decompose some three to seven times faster than the stems. Stems decayed significantly faster in Lake Sortesø than in Lake Hampen, whereas decomposition of leaves was only significantly faster in Sortesø during the first six months of the study period. Concentrations of Zn, Pb, and Cd increased significantly in Phragmites leaves during decomposition. The actual contents of Zn and Cu were either relatively constant or decreased, whereas those of Pb and Cd increased. A simplified model showing the cycling of heavy metals in the littoral zone of the two lakes indicates that Lake Hampen is more sensitive to pollution with heavy metals than Lake Sortesø.

III. Heavy metal content of sewage effluent, sludge, soil, and pasture

Abstract Surface irrigation of pasture with treated sewage effluent at Templeton, Christchurch, for up to 16 years, had little effect on the heavy metal composition of the soil or pasture. Slightly higher levels of 0.1n HC1-extractable Zn, Cu, Co, and Mn in the effluent-treated soil did not increase levels of these elements in the pasture, and did not increase the Cd/Zn ratio. The absence of any marked changes in heavy metal content is attributed to the low levels of these elements in the raw sewage effluent, which is of domestic origin. It is concluded that at the present effluent application rate (840 mm/year) the scheme, without sludge disposal, has an essentially indefinite life span, in terms of heavy metal accumulation. If land application of the sludge is introduced, it would take at least 200 years for heavy metals to reach the recommended limit of 5% of the soil cation exchange capacity.