P. S. Hooda

A review of water quality concerns in livestock farming areas.

Post-war changes in farming systems and especially the move from mixed arable-livestock farming towards greater specialisation, together with the general intensification of food production have had adverse affects on the environment. Livestock systems have largely become separated into pasture-based (cattle and sheep) and indoor systems (pigs and poultry). This paper reviews water quality issues in livestock farming areas of the UK. The increased losses of nutrients, farm effluents (particularly livestock wastes), pesticides such as sheep-dipping chemicals, bacterial and protozoan contamination of soil and water are some of the main concerns regarding water quality degradation. There has been a general uncoupling of nutrient cycles, and problems relating to nutrient loss are either short-term direct losses or long-term, related to accumulated nutrient surpluses. Results from several field studies indicate that a rational use of manure and mineral fertilisers can help reduce the pollution problems arising from livestock farming practices. Several best management practices are suggested for the control of nutrient loss and minimising release of pathogen and sheep-dip chemicals into agricultural runoff.

Plant availability of heavy metals in soils previously amended with heavy applications of sewage sludge

Plant uptake is one of the major pathways by which sludge-borne potentially toxic metals enter the food chain. This study examined the accumulation of Cd, Cu, Ni, Pb and Zn in wheat, carrots and spinach grown on soils from 13 sites previously amended with sewage sludge. Winter wheat, carrots and spinach were grown consecutively under field like conditions. The results showed that plant availability of heavy metals differed widely among the crop species. The accumulation of Cd, Ni and Zn in the plants showed the greatest increases compared to their background levels. The Cu and Pb accumulation in the plants grown on sludge-amended soils showed only small increases compared to those grown on uncontaminated soils. Multiple regression analysis of various soil properties showed that the surest way to control the accumulation of metals in food plants is by controlling their concentrations in the soils. Furthermore, soils with a non-acidic pH and a clayey texture tended to achieve better control of metal accumulation in food plants compared to those with an acidic reaction and a coarse texture. Metal concentrations in the plants generally correlated well with those extracted from soils in 0·005 M DTPA, 0·05 M EDTA-(Na)2, 1 M NH4NO3 and 0·05 M CaCl2. The EDTA, however, proved to be a more reliable and consistent test in predicting the accumulation of metals in the plants. The results also showed that liming soils to pH 7 effectively reduced the metal contents in carrots and spinach, but liming to pH 6·5 had little effect on metal concentrations in wheat grain.

Manuring and fertilization effects on phosphorus accumulation in soils and potential environmental implications

Abstract Phosphorus application as manure to agricultural soils in intensive livestock farming and arable cropping systems often exceeds P offtake by crops. This surplus could lead to P accumulation in soils, making them long-term diffuse sources of P loss to water. We investigated the impact of a range of manuring and fertilization practices in intensive farming systems on the accumulation of P in soils, soil test phosphorus (STP), distribution of organic and inorganic P, P-sorption capacity and degree of soil saturation with P (DSSP). The results from the 10 long-term sites investigated showed increases in both total soil P content and STP values (Olsen-P and Mehlich-3 P), as a result of P surpluses. The net total P accumulation in the soils across the sites ranged from 16 to 232 kg P ha−1 year−1. The effects of long-term P surpluses were a significant reduction in P-retention capacity and increase in DSSP. The sites investigated would attain 25% DSSP in 10–150 years, depending upon the size of P surplus and sorption capacity. A combination of large P surplus and low P-sorption capacity could saturate soils to 25% DSSP within 10–30 years. The values of Olsen (85 mg P kg−1) and Mehlich-3 (305 mg P kg−1) extractable-P predicted for the 25% DSSP are likely to result in environmentally significant P losses.

Cadmium and lead sorption behaviour of selected English and Indian soils

Abstract The environmental impact of metal additions to a soil depends on the metal sorption ability of the soil. This study compared the Cd and Pb sorption abilities of some selected English and Indian soils. The results showed that the English soils generally sorbed Cd and Pb more strongly and in greater amounts compared to the Indian soils. Soil pH, CEC, contents of organic matter, clay and CaCO 3 were all positively correlated with Freundlich metal retention parameters (log K f and 1/ n ) whereas the sand content had a negative correlation. The contents of free Fe oxide (FFeO) and easily reducible hydrous Mn oxide (HMnO) had no major influence on Cd and Pb sorption by these soils, except HMnO on 1/ n for Cd sorption. Correlation and regression analyses indicated that clayey textured soils with neutral to alkaline pH or soils with appreciable (≥10%) amounts of CaCO 3 and organic matter would be the most suitable for the disposal of Cd and Pb containing wastes. The results also showed that the application of a sewage sludge significantly increased the sorption of both Cd and Pb by all English soils, but a considerable decline in Pb sorption by most Indian soils was observed.

The effect of liming on heavy metal concentrations in wheat, carrots and spinach grown on previously sludge-applied soils

Liming is often recommended to minimize the plant uptake of potentially toxic elements from sludge-amended soils. In outdoor experiments conducted during 1989-91 in a rural location, near Brentwood (UK), wheat, carrots and spinach were grown on soils from a wide range of sites previously amended with heavy applications of sewage sludge. The objective of these studies was to examine the effect of liming on the accumulation of sludge-borne metals in the crop plants. The results showed that liming the soils to pH 7 prior to sowing significantly reduced metal concentrations in carrots and spinach, although the reduction appeared to be greater for Cd, Ni and Zn than for Cu and Pb. The wheat crop was grown on soils which had been limed 2 years previously, and the average pH of these soils was 6.5 compared to a pH value of 5.95 in the unlimed soils. This comparatively small pH difference between limed and unlimed soils (6.50-5.95) generally had little influence on metal contents in wheat. These results suggested that maintaining the soil at pH 7 is better than pH 6.5 for minimizing the accumulation of potentially toxic elements from soils which have received relatively high levels of sludge application over many years. The data for winter wheat suggested either that metal uptake into the grain was not sensitive to differences in soil pH or that a relatively small residual effect of past liming was not high enough to reduce metal uptake.

Opportunities and challenges in the use of coal fly ash for soil improvements – A review

Coal fly ash (CFA), a by-product of coal combustion has been regarded as a problematic solid waste, mainly due to its potentially toxic trace elements, PTEs (e.g. Cd, Cr, Ni, Pb) and organic compounds (e.g. PCBs, PAHs) content. However, CFA is a useful source of essential plant nutrients (e.g. Ca, Mg, K, P, S, B, Fe, Cu and Zn). Uncontrolled land disposal of CFA is likely to cause undesirable changes in soil conditions, including contamination with PTEs, PAHs and PCBs. Prudent CFA land application offers considerable opportunities, particularly for nutrient supplementation, pH correction and ameliorating soil physical conditions (soil compaction, water retention and drainage). Since CFA contains little or no N and organic carbon, and CFA-borne P is not readily plant available, a mixture of CFA and manure or sewage sludge (SS) is better suited than CFA alone. Additionally, land application of such a mixture can mitigate the mobility of SS-borne PTEs, which is known to increase following cessation of SS application. Research analysis further shows that application of alkaline CFA with or without other amendments can help remediate at least marginally metal contaminated soils by immobilisation of mobile metal forms. CFA land application with SS or other source of organic carbon, N and P can help effectively reclaim/restore mining-affected lands. Given the variability in the nature and composition of CFA (pH, macro- and micro-nutrients) and that of soil (pH, texture and fertility), the choice of CFA (acidic or alkaline and its application rate) needs to consider the properties and problems of the soil. CFA can also be used as a low cost sorbent for the removal of organic and inorganic contaminants from wastewater streams; the disposal of spent CFA however can pose further challenges. Problems in CFA use as a soil amendment occur when it results in undesirable change in soil pH, imbalance in nutrient supply, boron toxicity in plants, excess supply of sulphate and PTEs. These problems, however, are usually associated with excess or inappropriate CFA applications. The levels of PAHs and PCBs in CFA are generally low; their effects on soil biota, uptake by plants and soil persistence, however, need to be assessed. In spite of this, co-application of CFA with manure or SS to land enhances its effectiveness in soil improvements.

The potential impact of geophagia on the bioavailability of iron, zinc and calcium in human nutrition

Geophagia, the deliberate ingestion of soil, is a complex eating behaviour with obscure aetiology and numerous health/medical problems. It is conventionally assumed that geophagia may help supplement mineral nutrients in individuals with limited intake of trace elements such as Fe and Zn. This view, however, has largely been based on the bulk nutrient composition of geophagic materials and the assumption that these nutrients are potentially available for absorption in the body. We have tested this assumption by equilibrating five geophagic materials collected from Uganda, Tanzania, Turkey and India with mineral nutrient concentrations and conditions similar to the gastrointestinal tract. The results showed that all five geophagic materials, regardless of their composition, sorbed large amounts of Fe and Zn across a range of dietary intake scenarios, even under acidic conditions (pH 2) similar to the stomach. However, significant amounts of Ca desorption were observed from calcareous soil samples. The findings show that while calcareous geophagic materials may supplement Ca, geophagia can potentially cause Fe- and Zn-deficiency. This is consistent with mineral nutrient deficiency problems observed in clinical nutrition studies conducted amongst geophagic populations.

Parameter selection and testing the soil water model SOIL

Abstract The soil water and heat simulation model SOIL was tested for its suitability to study the processes of transport of water in soil. Required parameters, particularly soil hydraulic parameters, were determined by field and laboratory tests for some common soil types and for soils subjected to contrasting treatments of long-term grassland and tilled land under cereal crops. Outputs from simulations were shown to be in reasonable agreement with independently measured field drain outflows and soil water content histories.

Trace metals and their source in the catchment of the high altitude Lake Respomuso, Central Pyrenees.

Lake Respomuso is a dammed lake of glacial origin at 2200 m altitude in the Central Pyrenees. This study investigated the source of a number of trace elements (As, Cd, Co, Cu, Mn, Ni, Pb and Zn) in its catchment and their possible link to the local geology. Altogether 24 sediment and 29 water samples were collected from all major streams feeding the lake. The sediments were analysed for trace elements, major mineral components, minerals and organic matter whilst water samples were analysed for dissolved metal concentrations. The trace element levels in the catchment sediment and water were relatively high compared to other similar altitude sites, with concentrations in the headwaters being generally higher than in the lower basin because of the source being concentrated in these areas. The principal component analysis revealed that the source of sediment-bound trace elements in the Lake Respomuso catchment is geogenic, and originated possibly in the sulphide minerals from slate formations. Except at one site, none of the water samples exceeded the WHO drinking water guideline for arsenic. Arsenic in water was significantly correlated with its concentration in the sediments, possibly due to the oxidation of arsenic bearing minerals. The dissolved concentrations of all other trace elements were generally lower than the WHO drinking water guide values and they were not related to their sediment concentrations. The As, Cd, Ni contents in sediment from several catchment streams exceeded their sediment quality thresholds. This geogenic source may pose risk to the stability of fragile local biodiversity and to the wider environment in the valley bellow particularly if the metals are mobilised, possibly due to environmental change.

Sorption of Cd and Pb by selected temperate and semi-arid soils : effects of sludge application and ageing of sludged soils

Five soils from semi-arid regions of India and 5 soils from England were compared with regard to their ability to sorb Cd and Pb when mixed with sewage sludge and as unsludged controls. The application of sewage sludge at 150t ha−1 significantly increased the amount of Cd retained by the soils. The sorption data were statistically best-fit to the linearized Freundlich equation and the slopes of the isotherms were steeper with sludge application, indicating an increased affinity for Cd in the soil-sludge mixtures. A similar trend in Pb sorption was also observed for the English soils following the sludge treatment. In contrast, most of the Indian soils showed a decline in Pb sorption following the sludge application. Liming an acidic English soil to pH 7.0 was shown to increase its metal sorption capacity.The longer-term persistence of these observed effects of sewage sludge addition on metal sorption by soils was investigated in two sludge-soil mixtures maintained under experimental conditions for up to 450 days. Samples of these soils taken 1,60 and 450 days after the mixing with the sludge were batch equilibrated with Cd and Pb and it was found that the metal retention in both soils decreased significantly over this time period.