Brian E. Davies

Trace element content of soils affected by base metal mining in Wales

Abstract During the nineteenth century water-borne ore particles and dissolved heavy metal salts from base metal mining (now defunct) in Wales caused the poisoning of animals and crops in river flood plains while smelter smoke affected higher ground. Reports of such poisoning are now rare. Soils once exposed to pollution were investigated. Control samples from a valley devoid of mines or mineralisation allowed the establishment of normal trace element values whence anomalous values in other soils were identified. Enhanced levels were found within the mining areas of total cadmium, lead, silver, zinc and, sometimes, copper in alluvial soils and high lead in slope soils: the pattern of enhancement was controlled by the composition of local ores. High total trace element values were reflected in high plant-available values. Thus enhanced amounts of heavy metals enter the food chain but their effects are unknown.

A graphical estimation of the normal lead content of some British soils

Abstract Soil Pb values were examined from four areas of England and Wales where mining once caused environmental pollution. The % cumulative frequency distributions of the log10 Pb contents for each area were plotted on probability graph paper. A lower, linear portion of each curve was identified and separated and was interpreted as a lognormal population derived from non-contaminated soils. From the linear elements of the four graphs the geometric means and geometric deviations were calculated from which it was concluded that uncontaminated soils are unlikely to contain more than 110 mg Pb per kilogram dry soil and average soil Pb is 42 mg/kg. These results are compared with literature reports of the Pb content of soil.

Plant-available lead and other metals in British garden soils

Abstract An account is given of an investigation of the fertility status and heavy metal content of garden soils in England and Wales and the availability to and uptake of lead by radish generally, and by potatoes in two villages of contrasting epidemiological history. Intentional interference (i.e., cultivation) of gardens by man has resulted in a generally high level of fertility, but inadvertent additions of lead and other metals have resulted in many garden soils being contaminated. There are regional differences in fertility but not in heavy metal content. In rural areas, uncontaminated soils were associated with allotments and new gardens, and lead contamination was identified in urban and industrial areas as a result of pollution from vehicle exhausts, industry, mining and miscellaneous sources. Mature gardens in rural areas were also contaminated by lead and evidence is presented to support a hypothesis of increasing pollution with time, perhaps due to coal ash from chimneys. Radish absorbed soil lead and certain gardens produced plants the lead content of which was close to or above the legal limit of 2 mg/kg Pb. Potato was a weaker absorber of lead but plant contents still reflected lead contamination of soil. Consumption of vegetables from contaminated gardens could account for an appreciable proportion of the maximum safe daily intake of lead.

Heavy metal uptake from contaminated soils by six varieties of lettuce ( Lactuca sativa L.)

A replicated pot experiment is described in which six lettuce varieties were grown in four contaminated soils of different Cd, Cu, Pb and Zn concentrations. Webbs Wonderful absorbed least and All Year Round absorbed most Cd and Zn from all four soils. Uptake of both metals by all six varieties increased with increasing soil contents and leaf Cd and Zn concentrations were positively and significantly correlated. There was little evidence for a varietal control of the absorption of Pb and none for Cu, but a significant positive correlation between leaf Cu and Pb concentrations was observed.

Trace elements in vegetables grown on soils contaminated by base metal mining

Abstract Mining for lead and other base metals in England and Wales has left a legacy of heavy metal contamination of apparently productive fields and gardens in areas of prosperous and expanding towns. To assess whether vegetables grown on these soils absorb excessive quantities of heavy metals small experimental plots were established in northeast Wales and Derbyshire. Roots and aerial parts of lettuce, onion, carrots and Brussels sprouts were analysed for Pb, Zn, Cu and Cd. Pb tended to be retained in the roots but other metals were more mobile and cadmium accumulated in lettuce and carrot leaves. The Cd and Pb contents of edible parts constitute a possible risk to public health.

Heavy metals in soils and radish in a mineralised limestone area of Wales, Great Britain

Abstract Halkyn Mountain, Clwyd, Wales is a limestone area containing lead and zinc ores which were mined until quite recently. A survey of agricultural soils has revealed extensive contamination by cadmium, lead and zinc and, to a lesser extent, by copper. Gardens in the area are also similarly contaminated and the composition of radish grown in the gardens reflects this metal enrichment. Soil levels for both total and plant-available cadmium and lead are unusually high and some radish samples exceeded the statutory limit for lead in food.

Lead contamination of roadside soil and grass in Birmingham, England, in relation to naturally occurring levels

Lead was determined in soil and grass from transects across three main roads and one minor road in Birmingham, England. The pattern of enhancement of lead contents was consistent with aerial contamination by lead compounds from motor vehicle exhausts. Data from grass sampled during wet and dry weather suggested that approximately half the lead was present as a removable surface film on the grass blade. Generally, the lead content of the grass was not high enough to affect grazing cattle adversely but the growing of vegetables for human consumption might need regulation. The lead values for contaminated soil, although locally high, were within the normal range for British and American soils and, for comparable traffic volumes, were less than those reported in the U.S.A. Attention is drawn to inter-laboratory differences when reporting analyses of reference rocks and the implications for environmental research.

Heavy metal content of plants growing on soils contaminated by lead mining

During the nineteenth century several parts of Wales were intensively mined for lead, zinc and copper ores. Fields adjacent to and downstream from the mines became contaminated by air- and water-borne heavy metal compounds. Such fields still contain high concentrations of total lead, zinc and copper together with silver and cadmium, the chief ‘guest’ elements in lead and zinc ores. Extraction of the soils with dilute acetic acid suggested that contaminated soils contained more of these metals that were available to plants (Alloway, 1969; Alloway & Davies, 1971). Some studies of plant composition were made to confirm the evidence from soil extraction and to indicate the extent to which these metals were entering the food chain.

Trace metal contamination of soils and vegetables in Shipham, Somerset

Copper, lead and zinc ores have been mined in past years in many western counties of Great Britain leaving a legacy of extensive soil contamination. A survey of north-east Clwyd (Davies & Roberts, 1978) revealed that in the Halkyn Mountain area some 171 km 2 of land are contaminated by lead and 69 km 2 by cadmium (including 13 km 2 containing from 10 to 540 mg Cd/kg soil). The Mendip Hills of Somerset are an ancient leadzinc mining area similar in many ways to Halkyn Mountain and, after some reconnaissance sampling in 1972 and 1974, a trace element survey was initiated in 1977. Topsoil samples (174) were collected on an approximately regular 2× 2 km grid from a 600 km8 area of north Somerset including the Mendips (B. E. Davies and R. C. Ginnever, unpublished results). This survey revealed that the Mendips were generally contaminated by cadmium, lead and zinc. Highest soil lead values were found near Wells (11 g/kg) and Charterhouse (73 and 80 g/kg) but in the case of cadmium the survey revealed that some 2 km 2 of land around the village of Shipham contained values exceeding 10 mg Cd/kg. Preparatory to detailed investigations planned for 1979 a reconnaissance survey of soils and vegetables from the village was made. Meanwhile, the Department of the Environment announced the results of another (independent) survey which also demonstrated that Shipham possessed a considerable cadmium problem (e.g. McGinty, 1979). A full account of our survey of north Somerset will be published and this paper presents the results from the reconnaissance of Shipham.

Silver in Welsh soils: Physical and chemical distribution studies

Abstract Profile distributions of Ag and other metals (Cd, Cu and Pb) in contaminated and uncontaminated soils from west Wales, U.K. are presented. Background Ag levels were μ g Ag g −1 , whilst profiles contaminated by past mining activities contained up to 9 μg Ag g −1 . Silver showed a marked surface enrichment in all cases. Adsorption of AgNO 3 by various soil samples was satisfactorily modelled by the Freundlich isotherm equation. Values for k (a constant related to the binding capacity) ranged between 50 and 1450. The Langmuir isotherm equation gave a less satisfactory summary of the adsorption behaviour. Radioactive 110m Ag added to intact cores of an alluvial and a peat soil and subjected to leaching over one year (at the annual precipitation rate) remained in the surface layers; after this time 110m Ag was not leached appreciably below 40 mm. A chemical fractionation procedure for soil Ag was applied to the contaminated soils. In soils contaminated between 80 and 150 years ago there were negligible amounts of readily exchangeable Ag; nearly half the total Ag was “residual” (i.e., solubilised only in concentrated nitric acid). The two intact soil columns still contained a considerable proportion of the 110m Ag in the readily exchangeable form after one year, but most was bound in ‘acid-reducible’ or ‘oxidisable-organic’ forms. The evidence for a strong association between soil organic matter and Ag indicates that humus may control the availability of Ag in the short term and that mineral prospecting for Ag by the chemical analysis of soil humus may be a useful reconnaissance technique. Fixation in a residual fraction may be a mechanism which reduces the bioavailability of the element in the long term.