Contamination of agricultural soil by urban and peri-urban highways: An overlooked priority?

Highways are major, open and dynamic sources of contaminants that present a risk to adjacent agricultural soils. Urban and peri-urban soils are particularly at risk because of a greater density of nearby highways with high traffic volumes. In developing economies, these soils support valuable food production and income, while in more developed economies there is a growing interest in urban food production. This commentary highlights the need to better characterise the sources, pathways to and impacts of highway contaminants on agricultural soils and it suggests research priorities. Soil contamination from highways includes metals, toxic organic pollutants and plastics (including large amounts of tyre dust). Contaminants from vehicle emissions and from wear of vehicles and highways are transferred to soil in airborne particulates, dust, splash, spray and runoff. Contamination is greatest near to the highway edge but can extend to >50m. Levels of metals including As, Cd, Cr, Cu, Pb, Ni, Zn in some soils adjacent to highways may exceed thresholds above which there is a potential risk of harm to food production. Elevated levels of non-threshold carcinogens (e.g. polycyclic aromatic hydrocarbons (PAHs)) in soil adjacent to highways are widely reported, with significant attribution to highway emissions. Mitigation options include improved vehicle design and performance, porous asphalt pavements, physical and vegetative barriers and better drainage. Research priorities include: (1) targeted soil monitoring to identify where highway contamination already presents a significant risk of harm to food production and to identify and assess trends in response to mitigation measures; (2) studies to assess the role of tyre particulate in transporting and releasing contaminants that are hazardous to soil (3) assessment of the risk to soil from pesticides used in highway maintenance; (4) analysis to inform a new emphasis on controlling soil pollution by innovative highway design and maintenance.

An exploration of spatial risk assessment for soil protection: estimating risk and establishing priority areas for soil protection.

Methods for the spatial estimation of risk of harm to soil by erosion by water and wind and by soil organic matter decline are explored. Rates of harm are estimated for combinations of soil type and land cover (as a proxy for hazard frequency) and used to estimate risk of soil erosion and loss of soil organic carbon (SOC) for 1 km(2)pixels. Scenarios are proposed for defining the acceptability of risk of harm to soil: the most precautionary one corresponds to no net harm after natural regeneration of soil (i.e. a 1 in 20 chance of exceeding an erosion rate of <1 tha(-1)y(-1) and SOC content decline of 0 kg t(-1)y(-1) for mineral soils and a carbon stock decline of 0 tha(-1)y(-1) for organic soils). Areas at higher and lower than possible acceptable risk are mapped. The veracity of boundaries is compromised if areas of unacceptable risk are mapped to administrative boundaries. Errors in monitoring change in risk of harm to soil and inadequate information on risk reduction measures' efficacy, at landscape scales, make it impossible to use or monitor quantitative targets for risk reduction adequately. The consequences for priority area definition of expressing varying acceptable risk of harm to soil as a varying probability of exceeding a fixed level of harm, or, a varying level of harm being exceeded with a fixed probability, are discussed. Soil data and predictive models for rates of harm to soil would need considerable development and validation to implement a priority area approach robustly.

Soil monitoring in Europe: a review of existing systems and requirements for harmonisation.

Official frameworks for soil monitoring exist in most member states of the European Union. However, the uniformity of methodologies and the scope of actual monitoring are variable between national systems. This review identifies the differences between existing systems, and describes options for harmonising soil monitoring in the Member States and some neighbouring countries of the European Union. The present geographical coverage is uneven between and within countries. In general, national and regional networks are much denser in northern and eastern regions than in southern Europe. The median coverage in the 50 km x 50 km EMEP cells applied all over the European Union, is 300 km(2) for one monitoring site. Achieving such minimum density for the European Union would require 4100 new sites, mainly located in southern countries (Italy, Spain, Greece), parts of Poland, Germany, the Baltic countries, Norway, Finland and France. Options are discussed for harmonisation of site density, considering various risk area and soil quality indicator requirements.

Soil health in agricultural systems.

Soil health is presented as an integrative property that reflects the capacity of soil to respond to agricultural intervention, so that it continues to support both the agricultural production and the provision of other ecosystem services. The major challenge within sustainable soil management is to conserve ecosystem service delivery while optimizing agricultural yields. It is proposed that soil health is dependent on the maintenance of four major functions: carbon transformations; nutrient cycles; soil structure maintenance; and the regulation of pests and diseases. Each of these functions is manifested as an aggregate of a variety of biological processes provided by a diversity of interacting soil organisms under the influence of the abiotic soil environment. Analysis of current models of the soil community under the impact of agricultural interventions (particularly those entailing substitution of biological processes with fossil fuel-derived energy or inputs) confirms the highly integrative pattern of interactions within each of these functions and leads to the conclusion that measurement of individual groups of organisms, processes or soil properties does not suffice to indicate the state of the soil health. A further conclusion is that quantifying the flow of energy and carbon between functions is an essential but non-trivial task for the assessment and management of soil health.

Evidence for an intimate geochemical factor in the etiology of esophageal cancer.

Epidemiological data for esophageal cancer in the Butterworth District, Transkei, was used to calculate incidence contours which confirmed large variations within short distances (less than 5 km). High- and low-risk zones were demarcated, and a close relationship with underlying geology observed. The low-incidence zones in the study regions were underlain by dolerite intrusions, whereas higher-risk regions were on sedimentary strata. Analysis of rocks indicated that those from the higher-risk regions contain less copper, cobalt, and manganese. Soil samples were analyzed for boron, cobalt, copper, manganese, molybdenum, nickel, sodium, lead, vanadium, and zinc; the results also indicated a strong geochemical association with the disease. The concentrations of copper (P = 0.001), nickel (P = 0.001), and boron were markedly lower in the high-risk zones. Manganese, zinc, and molybdenum levels in soils also tended to be substantially lower in the high-risk zone.