PHEs, Environment and Human Health

The atmosphere represents a complex system influenced by the chemical and physical processes that occur at the Earth surface. These processes include emissions, transport, lifetimes and fates of several anthropogenic and biogenic/geogenic chemicals emitted from a wide variety of sources. Among these chemicals, some are considered air pollutants, i.e. any substance present in ambient air and likely to have harmful effects on human health and/or the environment as a whole. Metals, and in general elements, are natural components of the earth’s crust and constituents of all ecosystems. In the atmosphere, they are mainly related to particle phase but also they can be present in a liquid phase due to the dissolution of aerosol particles in the water drops. Whatever their origin, both natural and anthropogenic, most elements, and in particular heavy metals, are dangerous because they tend to bio-accumulate in the human body.

This chapter describes a general overview on elements and their sources and potential effects on human health in atmosphere. Furthermore, considering the increase of the interest on biological fraction of PM, a briefly description of bioaerosols will be made. Recently, the number of evidence that describes how this fraction may play a key role in the effects of PM on biological systems with negative impacts on human health and ecosystem functioning are increased.

Mathematical model applied to air pollution studies will be briefly described. Mathematical models (dispersion and transport model), that predict the concentration and the dispersion of primary and secondary pollutants in atmosphere, represent a fundamental tool in the atmospheric studies to develop health and/or environmental risk assessment and various control strategy actions. Moreover, some specific elements (Sb, Tl, V and Be) will be discussed investigating the effects on health, main sources application and reviewing the most recent studies.

Estuaries and coastal zones are dynamic transitional systems which provide many economic and ecological benefits to humans, but also are an ideal habitat for other organisms as well. These areas are becoming contaminated by various anthropogenic activities due to a quick economic growth and urbanization. This chapter explores the sources, chemical speciation, sediment accumulation and removal mechanisms of the harmful elements in estuarine and coastal seawaters. It also describes the effects of toxic elements on aquatic flora and fauna. Finally, the toxic element pollution of the Venice Lagoon, a transitional water body located in the northeastern part of Italy, is discussed as a case study, by presenting the procedures adopted to measure the extent of the pollution, the impacts on organisms and the restoration activities.

Soil is a very complex and vulnerable system; a living surface soil is a mixture of solid matter, water, air, and biota components. Human activity nowadays involves such high level of environmental interventions which often irreversible damages and destroys the soil. During the past century, as a consequence of industrial, agricultural and urban activities of man, soil and water resources were contaminated with potentially harmful trace elements (metals and metalloids). As a consequence of pollution the fertility of soils, the most important feature of the soil for mankind was changed adversely. Trace element content and status of agricultural soils may influence plant uptake and concentration of the given element in the tissues of food and fodder crops, thus affecting the quality of food and drinking water with potential implications to human health. After demonstrating the sources of potentially harmful trace elements in agroecosystems the characteristics, ecological significance, environmental exposure, behaviour in soil and biological impacts of the seven most commonly occurring potentially harmful trace elements (As, Cd, Cr, Cu, Hg, Pb and Zn) will be presented in this chapter. Focusing on soils and plants, their accumulation is followed up in foods, and their impacts are summarized on human organism. Case studies are presented to demonstrate the presence of potentially harmful trace elements in urban and industrially contaminated soils, their accumulation in plants, and discussing the possibility of phytoremediation.

Forest ecosystems differ from agroecosystems, in the first place by the established vegetation cover of deciduous or needle trees, associated with a specific biochemical cycling of forest organic matter. The presence of a forest floor (litter O and humus-rich A horizons) introduces additional pathways of biogeochemical cycling of potential harmful major and trace elements (PHTE), with respect to soils under agricultural land use. Moreover, unlike agroecosystems, forest soils are predominantly affected by only one way of PHTEs inputs, deriving from atmospheric deposition. Aged and established forests are generally in a state of equilibrium with respect to elemental cycling. In such forest soils, especially in their deep horizons which are most often little affected by any contamination, PHTE contents are fairly close to the initial natural pedo-geochemical background concentrations. Consequently, they can be used as a reference for other soils developed in the same parent material, but under agricultural land use and affected by anthropogenic contaminations. Exceptions are forest soils located in the proximity of industrial or mining areas, which are more exposed to short-range industrial atmospheric fallout.

Forest soils often have a lower buffering capacity against acidification than agricultural soils due to the adding of acid-neutralizing amendments (fertilization, liming, and compost) to the latter. In strongly acid forest soils, the risks of mobility of PHTEs are well-established and migration may occur in soluble, pseudo-soluble or particulate forms. Soil acidity may lead to high levels of Al and Mn, representing additional risks of aluminium or manganese toxicity. The forest floor represents a particular metal trapping medium in soils. When a mor-type humus layer is present at the surface of forest soils, exogenous pollutants accumulate, as a first step, in a fully organic surface horizon. But the fate of contaminants in terms of permanent retention, or subsequent partial or even full release, and times of retention are items that are still under debate. In the particular case of podzols with strongly acidified soil conditions, PHTEs are susceptible to migrate to depth and to a part intercepted (long-term, permanently?) in the B horizons whereas another part may leach out of the soils and possibly transferred to the groundwater.

For a good understanding and a relevant interpretation of PTHE concentrations through the soil profile, in terms of accumulation or impoverishment, the limits of the morphological horizons must be respected during sampling. Such horizons may be of small thickness (for instance Bh horizons in podzols), but they can demonstrate substantially contrasted concentrations, for instance in the case of strongly differentiated soils (cf Table 4.3). Taking into consideration the characteristic processes involved in the formation of soil horizons, is essential for a better insight into mechanisms and pathways of cycling of PTHEs. Hence, for a valid assessment of the presence, distribution and fate of PTHEs in forest soils, and in order to allow an appropriate comparison with anthropogenic contaminated agricultural soils, it is crucial to take account of different soil parameters, such as the nature of the parent material, pedological characteristics and specific physico-chemical conditions. Moreover, and surely, it is essential to adopt a soil sampling strategy that is adapted to the aims and/or different parts of multidisciplinary study programs.

Soils are essential components of the environment therefore; soil quality must be controlled and preserved. However, the increased concentration and distribution of potentially toxic elements (PTE) in soils by anthropogenic activities of industrial and mining resources are causing worldwide concern. The anomalous concentration of PTE may affect the soil’s environment, reducing it’s quality and therefore pollution which can be followed by an eventual accumulation through the food chain. This implies a serious risk for crops, livestock and human health. There is an increasing need to apply innovative technologies of prevention, monitoring, risk assessment and remediation, more sustainable and economical, in the context of mining site soils.

In this chapter, the impact of PHEs from abandoned mine sites on the environment is discussed through case studies from Europe (NE Italy). The environmental effects recognized for these specific sites could be valid other mining sites worldwide. Some case studies highlight the toxicity assessment of contaminated soils from abandoned mining areas; others focus on the metal uptake and translocation ability in plants that can produce adverse effects on plant morphology and health and biological soil quality evaluation of abandoned mining site.

Throughout the human history, the anthropic activity inevitably leads to a legacy of increased PHE concentration in the environment. Nowadays the urban environment can be considered the main habitat for humans. Therefore, the acknowledgment and the understanding of the impact of PHEs in urban soils and dusts is imperative in order to develop a plan for the sustainable management of urban areas, which should limit this impact on human and environmental health. A historical background regarding urban soil contamination is presented, along with an overview of the PHEs and PGEs found in urban soils. As humans are daily exposed to PHEs present in air, water and soil, studies are focusing on their long-term effects and on the toxicological impact of PHE (PHEs’) combinations, rather that of single elements. The importance of a comprehensive assessment of PHEs in urban soils and dusts, including their bioavailability, is discussed.

This chapter aims to offer an overview of the main remediation methods of potentially toxic elements in contaminated soils, mainly heavy metals, metalloids and radionuclides, focusing on their essential characteristics, advantages and limitations. It consists of two main groups of technologies: the first group dealing with containment and confinement, minimizing their toxicity, mobility and bioavailability. Containment measures include covering, sealing, encapsulation and immobilization through solidification (cement-based, polyethylene and resine binders, bituminization or asphalt batching and vitrification or glassification) and stabilization with inorganic and organic amendments. The second group, remediation with decontamination is based on the remotion, clean up and/or destruction of contaminants. This group includes mechanical procedures (excavation, transport and disposal to landfills), physical separations, chemical technologies such as soil washing with leaching or precipitation of potentially toxic elements, soil flushing, thermal treatments (desorption, pyrometallurgical processes and incineration) and electrokinetic technologies (electromigration, electroosmosis, electrophoresis and combinations of electrokinetics with other techniques). There are also two approaches of biological nature: bioremediation (biosorption, bioreduction, biomineralization and bioleaching-with some examples from Korea) and phytoremediation (phytoextraction, including chelate-assisted phytoextraction, phytostabilization, phytoremediation in mining activities -with examples from Portugal, Spain, Ecuador, Peru and Chile mainly-, phytovolatilisation and phytomining).

Chemical elements exist naturally in the environment with different concentrations. However, human activities can increase these concentrations, what represent a serious threat to ecosystems and to the human health. In soil, the chemical elements are distributed in different physicochemical forms; inorganic species, organic complexes, adsorbed on solid phases or as constituents of solid phases with different solubility degrees. Plants can absorb only the elements present in the so-called available fraction, which is associated to the exchange complexes and soluble fractions in the soil solution. Absorption, translocation and accumulation of the elements in the plants depend on the species and ecotype as well as on the plant organ, climatic conditions and season of the year. Usually, essential elements (macro and micro-nutrients) are absorbed and translocated to the aerial part of the plant, while toxic elements are retained in the roots, however some hazardous elements are also transported to shoots. High concentrations of toxic elements in the plants can affect their biological processes and/or trigger different physiological responses to combat the oxidative stress (e.g. antioxidative enzymes, glutathione, phytochelatins). The elements accumulated in edible organs of crops or in spontaneous plants represent the major entry point in the food chain. Even at concentrations below phytotoxic levels, hazardous elements can pose health risks for humans due to the augmentation effect along the food chain. The objective of this chapter was to elucidate/clarify the pathways of the chemical elements in the soil-plant-human system as well as the physiological mechanisms that plants develop to respond to the absorption and accumulation of hazardous chemical elements.

Food is our energy source and limited access to food impacts health in multiple ways. Typically, food is thought to have a positive impact on health by providing energy and essential nutrients to living beings. Despite this, often it is so detrimental to health and several foodborne diseases clearly indicate that food safety not only involves availability and access to food, but that the food must be wholesome as well. The threat to food security is depending on urbanization, income disparity, overpopulation, ecosystem degradation, animal health, etc.

Trace elements are essential components of biological structures, but at the same time they can be toxic at concentrations beyond those necessary for their biological functions. Variation in uptake in the gastrointestinal tract varies depending on chemical form, salt or ionic form, dietary matrices, and interactions with other nutrients.

Adverse effects can occur from too low or too high intake of an essential element. Therefore, it may not be possible to arrive at recommendations that working for all individuals, since some persons with genetically determined metabolic disorders may require intakes that are higher or lower than those indicated by the acceptable range of daily oral intake.

Important advances has been made in the last decades in our understanding of the environmental biochemistry, biological effects and risks associated with trace elements.

This chapter provides a general picture on the essentiality of trace elements as a function of their role as catalytic or structural components of larger molecules, trying to focus the attention on the fine line between Essentiality and Toxicity. A general survey, because of the impossibility to draw a common guideline for all elements considered, is reported for each elements, that is on their geochemistry and biological functions in humans. In details, for each element an account is given of the mean total quantity accumulated by the human body, the distribution in the main organs, the most important pathways for their uptake and the recommended daily intake.

Nowadays risk assessment is assuming more and more importance in the solution of problems connected with land sustainability and human health. Indeed, the risk assessment criteria are applied to identify and classify the various sites on the basis of the actual land characteristics, and the potential hazard to exposed population.

There are various exposure pathways of toxic substances to general population: direct pathways are soil ingestion, dust inhalation, dermal contact; indirect ingestion through the food chain is one of the most important pathways for the entry of PHEs into the human body.

In order to avoid possible consequences to humans and the environment, it is necessary to investigate the source, origin, pathways, distribution in all the environmental compartments, and to ascertain if metal bioaccumulation is likely to occur, affecting human health.

Risk assessment procedures include two components, the Environmental Risk Assessment and the Human Health Risk Assessment. The former has been used mainly for comparative and priority setting purposes with reference to contaminated sites. The latter refers to the possible consequences of human exposure to contaminant sources. The ecological risk is generally considered a second priority in comparison to human health risk.

Estimate of exposure levels is a central step in Ecological Risk Assessment to evaluate ecotoxicity risks posed by PHEs. For example, agricultural soils contaminated with metals result in elevated uptake and transfer of metals to vegetables; consequently, severe health hazard can be caused by the consumption of metal-contaminated vegetables. Bioaccumulation of heavy metals in edible parts of vegetables is thus responsible for major health concern.

Human health risk assessment has been used to determine if exposure to a chemical, at any dose, could cause an increase in the incidence, or adverse effects, on human health.

Biological monitoring is a promising method of assessing environmental and human health risk by analysing PHEs concentration in environmental matrixes (e.g. plants, animals), or in human tissues (hairs, nails), or in a biological matrix (blood, urine). Concerning human health, biological monitoring is usually described as the measurement of a particular chemical substance, or a metabolite of that substance, in a suitable biological matrix (e.g. blood, urine, serum, and tissues such as hairs, nails, sweats), that act as an effective biomarker, allowing identification of potential hazards.

Examples of how the risk assessment process may be carried out are given with reference to exposure levels and exposure-response relationships for the contaminants of concern.

Potentially harmful elements, or more generally trace elements, are now considered to be among the most effective environmental contaminants, and their release into the environment is increasing since the last decades. Metals released by different sources, both natural and anthropic, can be dispersed in the environment and accumulated in plants and, ultimately, in human body, causing serious health problems as intoxication, neurological disturbances and also cancer. Widespread interest in trace elements has risen as major scientific topic only over the last 50 years, when it was realized that some elements were essential to human health (e.g. Fe, Cu, Zn), whereas some others were toxic (e.g. As, Hg, Pb), and likely responsible for serious human diseases, with frequent lethal consequences.

Since that time, great progresses in knowledge of links between environmental geochemistry and human health have been achieved, in combination with epidemiology.

The effects of most trace metals on human health are not yet fully understood, partly because of the interactions between them, and partly because of the complex metabolic reactions in the human body. Despite the copious research addressed to this topic, there is still a paucity of quantitative information on the relations between elements in soils and human health. Much is known about the functions of most elements in human body, but there is increasing evidence that the interactions among them are more complex than originally thought. Uncertainty is still prevailing, particularly with non essential elements that are “suspected” to be harmful to humans.

The nonessential elements As, Cd, Hg, Pb have attracted most attention worldwide, due to their toxicity towards living organisms. Other elements (Al, B, Be, Bi, Co, Cr, Mn, Mo, Ni, Sb, Sn, Tl, V, W, Zn) are likely harmful, but may play some beneficial functions not yet well known, and should be more investigated.