Peter W. Abrahams

Soils: their implications to human health.

This paper reviews how the health of humans is affected by the worlds soils, an association that to date has been under appreciated and under reported. Soils significantly influence a variety of functions (e.g. as a plant growth medium; its importance on the cycling of water; as a foundation for buildings) that sustains the human population. Through ingestion (either deliberate or involuntary), inhalation and dermal absorption, the mineral, chemical and biological components of soils can either be directly beneficial or detrimental to human health. Specific examples include: geohelminth infection and the supply of mineral nutrients and potentially harmful elements (PHEs) via soil ingestion; cancers caused by the inhalation of fibrous minerals or Rn gas derived from the radioactive decay of U and Th in soil minerals; and tetanus, hookworm disease and podoconiosis caused by skin contact and dermal absorption of appropriate soil constituents. Human health can also be influenced in more indirect ways as soils interact with the atmosphere, biosphere and hydrosphere. Examples include: the volatilisation of persistent organic pollutants (POPs) from soils and their subsequent global redistribution that has health implications to the Aboriginal people of the Arctic; the frequent detrimental chemical and biological quality of drinking and recreational waters that are influenced by processes of soil erosion, surface runoff, interflow and leaching; and the transfer of mineral nutrients and PHEs from soils into the plants and animals that constitute the human food chain. The scale and magnitude of soil/health interactions are variable, but at times a considerable number of people can be affected as demonstrated by the extent of hookworm infection or the number of people at risk because they live in an I-deficient environment. Nevertheless, it can often be difficult to establish definite links between soils and human health. This, together with the emergence of new risks, knowledge, or discoveries, means that there is considerable scope for research in the future. Such investigations should involve a multidisciplinary approach that both acquires knowledge and ensures its dissemination to people in an understandable way. This requires an infrastructure and finance that governments need to be responsive to.

The composition of snowfall, snowpack and meltwater in the Scottish Highlands ― evidence for preferential elution

Abstract Acidic snows in a small, remote, high-altitude snowpack in the Cairngorms, Scotland, give rise to meltwaters which are proportionally rich in sulphate and nitrate. As a consequence, the within-pack snows become proportionally rich in chloride, even though depleted in solute. Preferential elution appears to be a major process in the chemical evolution of snowfall and snowpack.

Geochemical evidence for atmospheric pollution derived from prehistoric copper mining at Copa hill, Cwmystwyth, mid-Wales. UK

This paper presents geochemical data from a blanket peat located close to a Bronze Age copper mine on the northern slopes of the Ystwyth valley, Ceredigion, mid-Wales, UK. The research objective was to explore the possibility that the peat contained a geochemical record of the pollution generateD by mining activity. Four peat monoliths were extracted from the blanket peat to reconstruct the pollution history of the prehistoric mine. Three different geochemical measurement techniques were employed and four copper profiles have been reconstructed, two of which are radiocarbon-dated. The radiocarbon dates at one profile located close to the mine confirm that copper enrichment occurs in the peat during the known period of prehistoric mining. Similar enrichment of copper concentrations is shown in one adjacent profile and a profile within 30 m away. In contrast, copper was not enriched in the other radiocarbon-dated monolith, collected approximately 1.35 km to the north of the mine. Whilst other possible explanations to explain the copper concentrations are discussed, it is argued that the high copper concentrations represent evidence of localised atmospheric pollution caused by Bronze Age copper mining in the British Isles. The results of this study suggest that copper may be immobile in blanket peat and such deposits can usefully be used to reconstruct atmospheric pollution histories in former copper mining areas.

Geophagy (soil consumption) and iron supplementation in Uganda.

Despite the often limited awareness of geophagy, the deliberate consumption of soil by humans, it is common in certain areas of the world. This paper reports the mineralogical and geochemical composition of geophagical materials collected from Uganda, and indicates the potential of such soils in supplying iron to the geophagist. In countries like Uganda where modern pharmaceuticals are either unobtainable or prohibitively expensive, ingested soils may therefore be very important as a mineral supplement for the health of individuals providing they are consumed sensibly. Alongside this argument is the fact that individuals in such poor countries are frequently iron‐deficient.

The Removal of Soluble Ions from Melting Snowpacks

Field and laboratory observations have indicated that the “fractionation” mechanism, whereby the bulk of the solute in seasonal snowcover is removed in the early meltwater fractions, is a differential process. Some soluble ions may be removed at faster rates than others. This process is known as “preferential elution”. Since the process is not yet universally accepted amongst scientists who engage in research into snowmelt chemistry, in this chapter we review the pertinent experimental work. Varying experimental conditions in real snowpacks often militate against reproducible elution sequences, although sodium and chloride are consistently found to be the least mobile ions upon melt. Laboratory experiments have provided more controlled conditions under which to examine the relative removal rates of soluble ions in meltwater. Those ions which are more soluble in ice are seen to be less mobile upon melt, whereas the ions which are eluted more rapidly may be regarded as being more strongly partitioned into the solute-rich surficial liquid, or quasi-liquid, layer. In real melting snowpacks, preferential elution of some ions by the meltwater can be masked by snowpack-scale hydrology.

The intake of lead and associated metals by sheep grazing mining-contaminated floodplain pastures in mid-Wales, UK: I. Soil ingestion, soil-metal partitioning and potential availability to pasture herbage and livestock.

This paper first evaluates the relative importance of the soil-plant-animal and soil-animal pathways of Zn, Cu and (especially) Pb investigated over a 15-month study period at 12 floodplain sites located within and downstream of the mineralised and historic mining area of mid-Wales, and secondly considers the implications of a sequential extraction procedure (SEP) undertaken on soils of varying particle size sampled from the study locations. Generally, very good agreement was found between the chemical partitioning of the three metals for each of the physical soil fractions subjected to the SEP. The availability of Pb to pasture vegetation, especially at the contaminated sites, is indicated with its associations with the more soluble (i.e. exchangeable and Fe/Mn oxide) soil phases, yet soil and/or plant barriers effectively restrict above-ground herbage concentrations of this metal. Consequently, with sheep ingesting soil at rates varying according to season from 0.1% to 44% or more of dry matter intake, the soil-animal pathway accounts for the majority of Pb consumption through most of the year, and at moderately and highly contaminated sites significant quantities of relatively soluble soil-Pb can be ingested at rates exceeding safety threshold limits.

SOIL INGESTION BY SHEEP GRAZING THE METAL ENRICHED FLOODPLAIN SOILS OF MID-WALES

Floodplain soils within and downstream from the mineralised and mined areas of mid-Wales, are contaminated by metals, especially Pb, because of historical and contemporary fluvial pollution. Rates of soil ingestion by sheep grazing these sites have been quantified to establish the relative importance of the soil-plant-animal and soil-animal pathway of metals. The highest rates of soil ingestion occurred during the winter/spring period. During March, soil ingestion exceeded 30% of the D.M. intake at 2 of the 11 sites investigated. The total daily intake of metals by sheep reflects the degree of soil metal enrichment, and is elevated during the winter/spring period, coincident with the higher rates of soil ingestion and the generally higher pasture herbage metal concentrations. Because the soil-plant transfer of Pb is low, ingested soil is often the major pathway of this metal to sheep. This is especially evident in March and May when on average 80.0 and 82.9%, respectively of the Pb intake was via soil ingestion. At one site in May, 97% of the Pb intake was attributable to ingested soil. Even when soil-plant transfers are not so low, as found for Cu and Zn, ingested soil can occasionally supply greater than 60% of these metals to the animal. However, despite the potential importance of soil ingestion, little is known about the availability to and absorption of soil-borne metals by animals.

Trace elements in snow samples from the Scottish Highlands: sources and dissolved/particulate distributions

Abstract Fresh snow samples were collected throughout a season at a high altitude (1080m) site in the NE Scottish Highlands and analysed for 14 trace elements in addition to the major element composition. Enrichment factors suggests three significant sources of the different elements, i.e. crust, seawater and anthropogenic inputs. Elements associated with anthropogenic and marine sources are in general soluble upon thawing (e.g. Br 98% dissolved) while elements from crustal sources are insoluble (e.g. Al 18% dissolved). Elements with mixed sources tend to show intermediate behaviour with average solubilities ranging from 27 to 96% for different elements. These solubilities are rationalized in terms of sources of the elements, their chemistry and the overall rainwater chemistry.

Spatial variability in the chemical composition of snowcover in a small, remote, scottish catchment

Abstract Fresh snowcover in a remote upland catchment is chemically heterogeneous. Coefficients of variation (Cof) for individual major ions range from 5 to 113%, assuming a normal distribution, or 1 to 144 % assuming a lognormal distribution. Aged snowcover is slightly more chemically variable, giving rise to Cof of 19–140 %, assuming a normal distribution, or 2–200 %, assuming a lognormal distribution. In general, the distribution of the concentration of major ions in snowcover is better described by the lognormal distribution. Both vertical and horizontal variability is observed in the chemical content of within-pack snows. Such heterogeneity has important implications for snowpack sampling. We suggest that rigorous methodologies should be devised for the sampling of fresh snowcover. The sampling of within-pack snows should also be performed under tight statistical constraints if representative estimates of the solute content of snowcover are to be obtained.

Geophagy and the Involuntary Ingestion of Soil

Geophagy or geophagia can be defined as the deliberate ingestion of soil. This is a practice that is common among members of the animal kingdom, including people. Any person who studies geophagy undertaken by humans will invariably confront a problem during their research. Few people will believe them. This is perhaps understandable for members of a developed urban society that is educated, has ready access to modern pharmaceuticals, and which has increasingly, in both a physical and mental sense, become more remote from soils. Yet many of these people will readily accept that wild animals deliberately eat soil. For example, television programs which feature wildlife may show animals consuming soil, with the presenter commonly stating that the soils are being eaten for their mineral nutrient content (although, as will be seen in the following sections, there are a variety of reasons why animals consume soil). But many people find it more difficult to accept that humans can deliberately eat soil. This ignorance of geophagy is not restricted to the layperson, because academic writers have used adjectives such as curious, odd, perverted, and strange when commenting on human geophagy. The use of such words demonstrates a misunderstanding of geophagy. The practice is common in certain human societies and can be readily found in many countries provided one has appropriate knowledge of the subject. An understanding of geophagy also allows an appreciation of the practice. There are perfectly sensible reasons as to why certain people deliberately eat soil, and the consumer can benefit from indulging in geophagy in a number of ways. It has been suggested that the practice should be considered within the normal range of human behavior (Vermeer 1986), an enlightened viewpoint that I personally support. However, before the reader hurries away to indulge in geophagy, a word of warning is necessary. Aside from the benefits that eaten soils can impart to the consumer, very serious health problems may also result. These benefits and banes of soil consumption are considered in more detail later in Sect. 18.6 of this chapter, along with other aspects of geophagy undertaken by humans. This information follows a discussion about geophagy that is practiced by members of the animal kingdom other than humans. In addition to geophagy, many animals (including humans) also accidentally ingest soil. In order to appreciate geophagy in its proper context, this involuntary ingestion of soil is considered first (see also Chap. 15, this volume).