A Review of Impacts of Global Climate Change on Bioaccumulations and Biomagnifications and the Implications on Human Ecology.

Kennedy W. Nyongesa

Institute of Climate Change and Adaptation (ICCA), University of Nairobi, Kitale National Polytechnic, Department of Mathematics and Applied Science :Corresponding email:kennyongesa@yahoo.com

Abstract

This paper reviews information from the literature on impacts of climate change including ecological drought. The paper highlights how climate change affects bioaccumulations, biomagnifications, and the implications on human ecology. Global climate change (GCC) is likely to alter the degree of human exposure to pollutants and the response of human populations to these exposures, meaning that risks of pollutants could change in the future. The paper, therefore, explores how GCC might affect the different steps in the pathway from a chemical source in the environment through to impacts on human health and evaluates the implications for existing risk-assessment and management practices. In certain parts of the world, GCC is predicted to increase the level of exposure of many environmental pollutants due to direct and indirect effects on the use patterns and transport and fate of chemicals. Changes in human behavior will also affect how humans come into contact with contaminated air, water, and food. Dietary changes, psychosocial stress, and co exposure to stressors such as high temperatures are likely to increase the vulnerability of humans to chemicals. These changes are likely to have significant implications for current practices for chemical assessment. Assumptions used in current exposure-assessment models may no longer apply, and existing monitoring methods may not be robust enough to detect adverse episodic changes in exposures. Organizations responsible for the assessment and management of health risks of chemicals therefore need to be more proactive and consider the implications of GCC for their procedures and processes.  In this paper,       a conclusion is drawn illustrated by a conclusive working model.

Key Words: Impacts, Global Climate Change, Bioaccumulations, Biomagnifications, Human Ecology.

Introduction

Historical Overview

Written records from up to 5 millennia ago provide evidence of climatic impacts on food shortages, famines, starvation, and deaths ; it must be noted that the historical data available for analysis are usually patchy. Often, the records do not associate occurred events with specific climatic conditions or are inherently biased. For example, there is little explicit information about specific population health benefits during benign climatic periods. Rather, the adverse periods and outcomes customarily attract attention and are usually well documented. In addition, information about heat wave impacts in earlier centuries is negligible, although information about deaths and suffering from periods of extreme cold often exists.

However, one must keep in mind that today’s wealthier and technology-rich societies differ in many ways from earlier societies. In several respects, modern societies might be more vulnerable to climatic stress than their predecessors. Potential vulnerabilities of modern societies include increasing deficit of suitable places for resettlement; increasing density of populations in vulnerable locations such as flood-plains and coasts; enhanced spreading of infectious diseases due to urbanization and globalization; fragility of complex urban infrastructure; disruptive changes in the Earth’s biosphere (land and sea overuse, disrupted nitrogen and phosphorus cycles, biodiversity losses); international tensions and economic crises. The nexus of drought, famine, and starvation has been the major serious adverse climatic impact over the past 12,000 years. Cold periods, more frequent and often occurring more abruptly than warm periods, have caused more apparent stress to health, survival, and social stability than the warming. Temperature changes of 1 to 2 °C (whether up or, more frequently, down) can impair food yields and influence infectious disease risks. Hence, the health risks in a future world forecast to undergo human-induced warming of both unprecedented rapidity and magnitude are likely to be great. Figure 1 shows the historical overview of Climate Change.

Variations in northern hemisphere temperature

Figure1: Historical Overview of Climate Change.

Source: National Academy of Sciences

Variations in northern hemisphere temperature, °C (relative to mean temperature during 1960–1980), averaged from multiple sources published since 2007. Averaging of hemispheric temperature is therefore only indicative. During early–mid Holocene (11–4 thousand years before present), for example, trends in regional temperatures differed, including prolonged cooling of much tropical ocean while warming for over 2 millennia in parts of Europe, China, and Scandinavia.

Global-scale Forcing of State Shift in Earth’s biosphere

Biological systems on local as well on global scale can shift rapidly from an existing state to a radically different state. A defined range of deviations from a mean condition over a defined period characterizes biological states. Either a “threshold” or a “sledgehammer” effect can cause this shift from one state to another. The former can be difficult to anticipate, because the critical threshold is reached slowly as incremental changes accumulate and the threshold value generally is not known in advance. By contrast, a state shift caused by a sledgehammer effect – for example the deforestation by logging – comes as no surprise. In both cases, the state shift (critical transition) is relatively abrupt and leads to new mean conditions outside of range of fluctuations observed in the previous state. The net effect is that once a critical transition occurs, it is usually irreversible. Recent theoretical work suggests that state shifts may be preceded by the following phenomena: a deceleration in recovery from perturbations (critical slowing down); an increase in the variance in the pattern of within-state fluctuations (asymmetry in fluctuations, changes in amplitude, etc.); increase in frequency of fluctuations (“flickering”).

Earth’s biosphere has undergone state shifts in the past over various time scales: last glacial-interglacial transition, “Big Five” mass extinctions and Cambrian explosion. One of the fastest planetary state shifts, and the most recent, was the transition from the last glacial (Pleistocene or Quaternary glaciations) into the present interglacial period (Holocene), which occurred over millennia. Glacial conditions had prevailed for ~100,000 years. Then, within approx. 3300 years, punctuated by episodes of abrupt, decadal-scale climatic oscillations, full interglacial conditions were attained. No completely satisfactory theory has been proposed to account for Earth’s history of glaciations. The causes of glaciations and deglaciation may be related to several simultaneously occurring global forcings, such as astronomical cycles, atmospheric composition, plate tectonics, and ocean currents. During last transition, most of the biotic change (extinctions, altered diversity patterns, new community assemblages, etc.) occurred within a period of 1,600 years beginning about 12,900 years ago. The ensuing interglacial state that we live in now has prevailed for the last 11,000 years.

Analysis indicates that all of the global-scale state shifts mentioned above coincided with global scale forcing that modified atmosphere, oceans, and climate and did not resulted from cumulative effect of many smaller-scale events that originate in local systems. Global-scale forcing mechanisms today are human population growth, habitat transformation and destruction, energy production and consumption, and concurrent climate change directly induced or significantly accelerated by human activities. All of these effects far exceed, in both rate and magnitude, the forcings evident at the most recent global-scale state shift, the last glacial-interglacial transition. Human population growth and per-capita consumption rate underlie all of the other present drivers of global change. The growth in the human population now (approx. 77,000,000 people per year) is 3 orders of magnitude higher than the average yearly growth from 10,000-10,400 years ago (approx. 67,000 people per year), and the human population is nearly quadrupled in the past century. If human fertility remains at 2005-2010 levels, the population will reach 27,000,000,000 by 2100. This population size is not thought to be supportable. As a direct result of human activities, approx. 43% of Earth’s land is now converted to agricultural or urban landscapes, with much of the remaining natural landscapes networked with roads. This exceeds the physical transformation that occurred at the last global-scale state shift, when approx. 30% of Earth’s surface went from being covered by glacial ice to being ice-free. The indirect global-scale forcings that have emerged from human activities include drastic modification of how energy flows through the global ecosystem. Humans commandeer approx. 20-40% of global net primary productivity (NPP) and decrease NPP through habitat degradation. Through the release of energy formerly stored in fossil fuels, humans have increased the energy ultimately available to power the global ecosystem. The vast majority of this “extra” energy is used to support humans and their domestic animals.

By-products of altering the global energy budget are major modifications to the atmosphere and oceans. The magnitudes and direction of both local-scale direct forcings and emergent global-scale forcings are not going to change any time soon. Therefore, the plausibility of a planetary state shift seems high. Some general consequences of such event can be gleaned from the results of past global-scale shifts. Biotic effects observed in the shift from last glacial to the present interglacial periods are most relevant to biological forecasting today. There were many extinctions; drastic changes in species distributions, abundances and diversity; and the emergence of new communities. New patterns of gene flow triggered new evolutionary trajectories, but the time since then has not been long enough for evolution to compensate for extinctions. However, even on evolutionary level human influences are felt by the Earth’s biosphere: super crops’ monocultures cover previously forested areas; thousands of breeds of domestic animals were created; pests and pathogens are being distributed globally; invasive species and feral domesticates interbreed and compete with native flora and fauna. Although ultimate effects of changing biodiversity and species compositions are still unknown, if critical thresholds of diminishing returns in ecosystem services were reached over large areas and at the same time global demands increased (as will happen when the population reaches ~11,500,000,000 by approx. 2060, widespread social unrest, economic instability and loss of human life will follow. Figure 2 exemplifies the concept of Climate Shift.

Climate shift

Figure 2: Climate Shift

Source: National Academy of Sciences.

Ecosystems, Climate Change and Human Ecology

Climate change is a change in the statistical distribution of weather patterns when that change lasts for an extended period of time (i.e., decades to millions of years). Climate change may refer to a change in average weather conditions, or in the time variation of weather around longer-term average conditions (i.e., more or fewer extreme weather events). Climate change can also be defined as change in the statistical properties (principally its mean and spread of the climate system when considered over long periods, regardless of cause. Within scientific journals, global warming refers to surface temperature increases while climate change includes global warming and everything else that increasing greenhouse gas levels affect. Global warming is a gradual process that threatens to have serious consequences over time, including elevated sea levels, crop failure and famine, changes in global rainfall patterns, changes to plant and animal populations, and serious implications for all aspects of human life especially health and Climate change is caused by factors such as biotic  and chemical processes, variations in solar radiation received by Earth, plate tectonics, and volcanic eruptions. Certain human activities have been identified as primary causes of ongoing climate change. Accordingly, fluctuations over periods shorter than a few decades, such as El Niño, do not represent climate change.

An ecosystem is a community of living organisms in conjunction with the nonliving components of their environment, interacting as a system. These biotic and abiotic components are regarded as linked together through nutrient cycles and energy flows. As ecosystems are defined by the network of interactions among organisms, and between organisms and their environment, they can be of any size but usually encompass specific, limited spaces although some scientists say that the entire planet is an ecosystem. Energy, water, nitrogen and soil minerals are other essential abiotic components of an ecosystem. The energy that flows through ecosystems is obtained primarily from the sun. It generally enters the system through photosynthesis, a process that also captures carbon dioxide from the atmosphere. By feeding on plants and on one another, animals play an important role in the movement of matter and energy through the system. They also influence the quantity of plant and microbial biomass present. By breaking down dead organic matter, decomposers release carbon back to the atmosphere and facilitate nutrient cycling by converting nutrients stored in dead biomass back to a form that can be readily used by plants and other microbes. Recent estimates show that climate change already causes at least 300,000 deaths per year worldwide. Three categories of risk can be differentiated:

  1. Direct impacts

Health and safety consequences of heat waves, floods, extreme weather events, increased concentrations of air pollutants.

  1. Risks through changes in ecological and biophysical systems

Changes in food yields leading to malnutrition (child stunting and death); altered flows, cleansing, and salinity levels of freshwater; changes in range, rates, and seasonality of climate-sensitive infectious diseases (climatic influences on pathogens, vector species, and intermediate-hosts animals).

  1. Social and economic disruptions and hardships

Diverse health disorders in climate-displaced groups; depression and despair in failing farm communities and disadvantaged indigenous and other marginalized groups. Health consequences of tension and hostilities due to climate-related declines in water, food, timber, and living space.

Bioaccumulations and Biomagnifications in Ecosystem Food Chains

Bioaccumulation is the process by which certain toxic chemical substances such as pesticides, heavy metals and polychlorinated biphenyls accumulate and keep on accumulating in living organisms, posing a threat to health, life, and to the environment. Also called bio-concentration, bioaccumulation occurs when an organism absorbs these substances at a rate faster than that at which the substances are lost by catabolism and excretion.

Biomagnification is the increase in concentration of a pollutant from one link in a food chain to another. It refers to the tendency of pollutants to concentrate as they move from one trophic level to the next.  For example in the process of biomagnification,  a fish at a lower trophic level accumulate mercury more rapidly than they excrete it, and every organism up the aquatic food chain contains more mercury than the one it just fed. 

In the case of mercury, through bioaccumulation mercury reaches higher concentrations in biota than are present in the environmental media in the first place. Under climate change, the structure and dynamics of marine food webs are in change. Arctic marine ecosystems are further affected by the reduction of sea- ice coverage and thickness. The ability to adapt to ecosystem shifts depends on the individual species, so the effect on mercury bioaccumulation depends on the food-webs structures and their responses to climate change. Trophic structures vary geographically and occur in two ways; either from the “bottom-up”, or from the “top-down”. “Bottom-up” changes links to primary or secondary productivity, such as plankton and other organisms, stratification, nutrient supply, light intensity or ice cover. These can have major effects on the production of organisms on a higher trophic level, but the complexity of such systems does not bring any confidence in future predictions under climate change. Changes in the top of the food- web, relate e.g., to the loss of sea ice cover and subsequent a shift in diet, habitats and/or migration pathways.

Changed biotope conditions and thus changed availability of current marine fish and mammals used for human consumption, as well as increased exploitation of natural resources, may have an influence on human exposure to mercury. Climate change may affect fish supply and the associations between habitual diet and blood concentrations for many contaminants. Furthermore, it is a serious concern that climate change will cause changes that affect the supply of traditional foods such as marine mammals and reindeer for people living in the Arctic. It has been concluded that the traditional foods and local products are more nutritionally adequate than the imported foods replacing them. Severely limiting the consumption of fish and seafood may do more harm than good by reducing the consumption of foods with health benefits and by increasing the consumption of alternative foods that have potential health risks such as increasing the possibility of obesity and diabetes.

Causes of Bioaccumulations and Biomagnifications

The release of toxic chemicals and pollutants into the environments such as the seas, air, and land results in the accumulation of toxins and harmful substances in the environment. The concentration of these toxic chemicals and pollutants seem to be very low when released in different environments, it eventually accumulates and gets absorbed by lower organisms in the food chains such as fish, earthworms, and plants. When the lower organisms are eaten by other organisms and the process goes up the trophic levels, biomagnifications occurs.

  1. Agricultural activities: According to the EPA, agricultural soil management practices can lead to production and emission of nitrous oxide (N2O), a major greenhouse gas and air pollutant. Activities that can contribute to N2O emissions include fertilizer usage, irrigation and tillage. The management of soils accounts for over half of the emissions from the Agriculture sector. Cattle livestock account for one third of emissions, through methane emissions. Manure management and rice cultivation also produce gaseous emissions. Agricultural pesticides, fungicides, herbicides, and chemical fertilizers, among other agricultural chemicals are highly toxic and often find way into the soils, rivers or lakes and the seas through surface storm water runoff. The primary agricultural inputs including pesticides, industrial by-product wastes, some fertilizers, and specific agrochemical products contain traces of heavy metals such as arsenic, cadmium, mercury, copper and lead. These substances cause severe health impacts to humans and aquatic animals such as fish when indirectly ingested and accumulate in the body tissues. Farming can deplete soil carbon and render soil incapable of supporting life; however, the study also showed that conservation farming can protect carbon in soils, and repair damage over time. The farming practice of cover crops has been recognized as climate-smart agriculture.

2.   Organic contaminants: Manures and Biosolids frequently contain nutrients including nitrogen, carbon, phosphorus and nitrogen. Furthermore, because they are industrially processed, they may also have within them contaminants such as personal care products (PPCPs) and pharmaceuticals. These products have been found in human and animal bodies and are believed to have negatively health impacts to wildlife, animals, and humans.

  1. Industrial manufacturing activities and pollution: The manufacturing processes of industries indirectly or directly release toxic and harmful substances that find a way to the soils, rivers, lakes and oceans. Industrial processes pollute the environment in several ways by emitting or discharging toxic pollutants into the environment that find way into the food chain, leading to biomagnifications
  2. Mining activities in the ocean: Mining activities in the deep sea is to extract minerals and metal ores like zinc, cobalt, silver, aluminum and gold destroy the oceans and the coastal regions as the mining processes generate scores of sulfide and selenium deposits in the waters. The toxicity levels build up and are absorbed by ocean creatures that are then consumed by organisms in the higher trophic levels of the food chain.

Anticipated Changes in the Source–Pathway–Receptor Relationship

For humans to be affected directly, chemicals must move through a pathway often called the source-to-receptor pathway. After being released from some source and moving through the environment, often being transformed by physical or biological factors in the process, chemicals must come into contact with and enter the body of a human. Once in the body, chemicals are subject to human toxicokinetic processes, ultimately coming in contact with some target tissue or molecular receptor to initiate an adverse outcome (Fig. 3). This chain of events is often complex, involving transformation of chemicals in the environment and their uptake and accumulation in organisms that play a role in exposing humans to those chemicals (e.g., consumption of contaminated fish). Changes in climate and associated changes in weather patterns, as well as non-climate-related drivers, are anticipated to affect various points in the source-to-receptor pathway, modifying how and to what extent humans are exposed to toxic chemicals and how they respond to harmful effects from those exposures.

Adaptation to GCC can influence the use and release of chemicals into the environment. For example, the types of pesticides, pharmaceuticals, and veterinary medicines used and the timing and frequency of their use will likely differ from today in response to changing disease and pest pressures resulting from GCC. Biocide use, for example, is likely to increase in response to increases in animal and plant pests and diseases that may arise from increasing temperature and humidity. Expected decreases in fossil fuel use resulting from greenhouse gas mitigation policies will likely reduce ground-level air pollution by particulate matter and ozone in urban areas, while shifts in the production of some types of biofuels may increase levels of air pollution in rural areas; also, their use may increase their combustion product exposures. In addition to changing human patterns of chemical use and other behaviors, GCC may affect the rates of formation of natural toxins (such as fungal and algal toxins) in the environment as well as the geographical distribution of these substances.

It is also likely that GCC will combine with other natural and anthropogenic factors to affect the transport and transformation of toxic chemicals in the natural environment. Increases in temperature can result in increased volatilization of persistent organic chemicals (e.g., at contamination sources such as buildings and electrical equipment), thereby increasing amounts subject to long-range transport. Increases in temperature and changes in moisture content are likely to alter the persistence of chemicals. Alterations in soil characteristics (organic carbon, dustiness) and hydrology may change how contaminants are transported around a terrestrial ecosystem as well as the dilution potential of contaminants in rivers and streams. Increases in the occurrence of extreme weather events, such as floods and droughts, will likely alter the mobility of contaminants. For example, flood events have been shown to transport dioxins, metals, and hydrocarbons from contaminated areas to noncontaminated areas. In agricultural areas, changes in irrigation practices in response to GCC could also move contaminants from water bodies onto land. Changes in the degree and duration of ice cover may affect the degradation of contaminants in some regions. For legacy contaminants, such as mercury, that have been released to the environment in the past and reside in soil and sediments, GCC may alter the environment in such a way that the substances are remobilized or released more rapidly.

Effects of GCC on human exposure to chemicals

Changes in the sources, fate, and transport of chemicals will have both positive and negative implications for contamination of food, drinking water supplies, air, and, hence, human exposure  However, very few studies have been performed to quantify the likely changes in exposure concentrations.  There are quantified effects of changes in the use, fate, and transport of pesticides, resulting either directly or indirectly from GCC, on surface water and groundwater concentrations.  It has been proved that concentrations of pesticides in surface waters and ground waters are likely to increase under GCC and that, for some pesticides, peak concentrations could increase by orders of magnitude. The indirect effects of GCC (i.e., effects on amount of pesticide applied and application timing) on surface-water exposure were found to be stronger than the impact of changes in the climate alone on chemical fate and transport. Additional studies of this type are needed for other classes of pollutant and other geographical regions.

Global climate change will affect not only the concentrations of toxic chemicals in water, food, and air, but also how humans interact with these media; this will also have implications for the degree of human exposure. For example, reduction in the availability of drinking water for many populations could change exposure to waterborne contaminants as human populations shift toward other sources of drinking water (e.g., water from water-reuse and reclamation systems) Changes in climate may also impact the amounts of time humans spend indoors and outdoors, influencing exposure to both indoor and outdoor contaminants. Figure 3 shows the Source–pathway–receptor relationship, showing interactions with both climate and non-climate stressors.

Figure 1.

Figure3: Source–pathway–receptor relationship, showing interactions with both climate and non-climate stressors. GCC=global climate change.

Source:  wileyonlinelibrary.com

Discussion

There is concern about these phenomena of bioaccumulation and biomagnifications because together they mean that even small concentrations of chemicals in the environment can find their way into organisms in high enough dosages to cause problems. Biomagnification, also known as bioamplification or biological magnification, is the increasing concentration of a substance, such as a toxic chemical, in the tissues of organisms at successively higher levels in a food chain. Human beings are at higher levels of most food chains In order for biomagnifications to occur, the pollutant must be long-lived, mobile, soluble in fats and biologically active .If a pollutant is short-lived, it will be broken down before it can become dangerous.  If it is not mobile, it will stay in one place and is unlikely to be taken up by other organisms.  If the pollutant is soluble in water, the organism will excrete it. Pollutants that dissolve in fats, however, may be retained for a long time. If a pollutant is not active biologically, it may biomagnify, but we really do not worry about it much, since it probably will not cause any problems. Pollutants of importance are plastics, radioisotopes (which may be both toxic and radioactive!) and oil.  

Plastics are eaten by many organisms and can cause mechanical injury, strangulation, or starvation.  Radioisotopes can damage biological molecules, particularly DNA, leading to cancer, other illnesses, or death.  Oil smothers aquatic organisms, cutting them off from oxygen.  It can also infiltrate the insulating feathers of seabirds (or fur of sea-going mammals) and cause them to die from hypothermia (or cause them to sink). Oil spills are a serious problem in marine environments.

Biological magnification often refers to the process whereby certain substances such as pesticides or heavy metals move up the food chain, work their way into rivers or lakes, and are eaten by aquatic organisms such as fish, which in turn are eaten by large birds, animals or humans. The substances become concentrated in tissues or internal organs as they move up the food chains. Bioaccumulants are substances that increase in concentration in living organisms as they take in contaminated air, water, or food because the substances are very slowly metabolized or excreted. The contaminants include heavy metals namely mercury, arsenic, pesticides such as DDT, and polychlorinated biphenyls (PCBs) compounds which are then taken up by organisms because of the food they consume or the intoxication of their environment.

Biomagnification stands for Biological Magnification, which means the increase of contaminated substances or toxic chemicals that take place in the food chains. These substances often arise from intoxicated or contaminated environments. These materials are present in a variety of household and industrial chemicals. The harmful substances then build up inside the organism’s cells. When organisms higher in the food chain consume the organisms containing the toxins below their trophic levels, the toxins gradually become concentrated in the higher food chain. Because this is a repetitive process in the ecosystem and throughout the entire food chain, the higher organisms are the ones that will accumulate most of the toxins. Higher organisms in most food chains include human beings.

There are two main groups of substances that biomagnify. Both are lipophilic and not easily degraded. Novel organic substances are not easily degraded because organisms lack previous exposure and have thus not evolved specific detoxification and excretion mechanisms, as there has been no selection pressure from them. These substances are consequently known as “persistent organic pollutants” or POPs. The other group is metals. Metals are not degradable because they are elements. Organisms, particularly those subject to naturally high levels of exposure to metals, have mechanisms to sequester and excrete metals. Problems arise when organisms are exposed to higher concentrations than usual, which they cannot excrete rapidly enough to prevent damage. Some persistent heavy metals are especially dangerous and harmful to the organism’s reproductive system. 

The following are some effects of bioaccumulations and biomagnifications on human ecology

1.         Impact on human health

Humans become more susceptible to cancers, liver and kidney failure, respiratory disorders, birth defects in pregnant women, brain damage, and heart diseases are a result of mercury, cadmium, lead, cobalt, chromium and other chemical poisoning. For instance, diseases like hepatitis and cancer have been attributed to consuming seafood that has been poisoned by mercury and polycyclic aromatic hydrocarbons (PAHs).

2.         Effects on reproduction and development of marine creatures

The various toxic chemicals and elements accumulate in the vital organs of the various aquatic creatures affecting their reproduction and development. For instance, seabird eggs are laid with thinner shells than normal, and can result in the birds crushing their eggs instead of incubating them. Selenium and heavy metals such as mercury also affect the reproduction of aquatic creatures such as fish as it destroys their reproductive organs. Besides, PCB’S (polychlorinated biphenyls) also biomagnifies and impairs reproduction and is considerable high in aquatic systems.

3.         Destruction of the coral reefs

The coral reefs are destroyed by cyanide that is used in leaching gold and in fishing. The reefs provide for spawning, feeding, and dwelling grounds for numerous sea creatures. When destroyed, the survival of aquatic creatures is highly compromised.

4.         Disruption of the food chains

Many sea creatures depend on the natural food chains for survival. When chemicals and other toxins are carried into the soils, rivers, lakes or oceans and taken up by various organisms, which disrupt the interconnected relationships within the food chains and food webs. It happens when small animals ingest or plants absorb the toxic elements after which large animals at higher trophic levels consequently eat them affecting the entire natural food chains. The creatures or plant in the food chains intoxicated with substances such as mercury, copper, chromium, cobalt, lead, selenium, among others. This leads to susceptibility to diseases, reproductive disorders, and even deaths. Humans are not exempted in this.

Conclusions and Recommendations

Impacts from climate change are happening now across the globe. Ecosystems and human communities are currently being affected. These impacts extend well beyond just an increase in temperature across the globe. Multiple sectors of our society, spanning across regional boundaries are being affected. Already impacted are are: water, energy, transportation, wildlife, agriculture, ecosystems, and human health.

The main current international agreement on combating climate change is the Kyoto Protocol, which came into force on 16 February 2005. The Kyoto Protocol is an amendment to the United Nations Framework Convention on Climate Change (UNFCCC). Countries that have ratified this protocol have committed to reduce their emissions of carbon dioxide and five other greenhouse gases, or engage in emissions trading if they maintain or increase emissions of these gases.

Human health is vulnerable to climate change. The changing environment is expected to cause more heat stress, an increase in waterborne diseases, poor air quality, extreme weather events, and diseases transmitted by insects and rodents. Ecosystems are also being affected by the changes that are occurring: habitats are being modified, the timing of events such as flowering and egg laying are shifting, and species are changing their home ranges. Changes are also occurring to the ocean. The ocean is absorbing about 30% of the carbon dioxide that is being released into the atmosphere from the burning of fossil fuels. As a result the ocean is becoming more acidic. Marine life is being affected by this ocean acidification. Along the coasts, higher sea levels cause these areas to be at a greater risk of erosion and storm surges.

Across the world, changes to water resources are of critical concern. In some regions, drought is an important factor and conditions are critically affecting local communities. In many regions, floods and water quality problems are likely to be worse because of climate change. Climate change has increased water stress. Few things are more important to human quality of life than easy access to clean water. Our food supply is dependent on climate and weather conditions. Although agricultural practices may be adaptable, changes like increased temperatures, water stress, diseases, and weather extremes create significant challenges for the farmers and ranchers who put the food on our tables.

Global climate change may affect multiple steps in the process of human exposure and harm to human health from chemical risks, including emissions from sources, transport and transformation in the environment, and human behaviors and vulnerabilities. For many chemical contaminants, a net increase in exposure is likely in certain regions of the world. While GCC will affect the fate and transport of chemicals in multiple and complex ways, in many cases the main climate-related drivers influencing human exposure will be changes in the types of chemicals used by society, alterations in the amounts and patterns of chemical use, and changes in the rates of formation of natural toxins in natural systems. Also, GCC will affect the way in which human populations interact with the natural environment so as to alter the degree of exposure. Alongside changes in exposure, changes in the sensitivity of humans to chemical exposure are expected due to factors such as increases in the levels of heat stress, psychosocial factors, suppression of the immune system, and alterations in nutritional status due to changes in diet and the quality of foodstuffs.

While each individual impact of GCC on chemical exposure and human sensitivity may not be highly significant and may occur in either a positive or a negative direction, the potential cumulative impacts of multiple influences could significantly alter risks to human health. Despite significant uncertainties, the preponderance of the current evidence suggests that many human health risks from chemicals may be increased in the future if a business-as-usual approach is adopted. Changes in risks are likely to be most significant for chemicals where microbes, plants, and lower animals are involved in the source-to-receptor pathway. Increases in risks are likely to be seen for the natural toxins that are produced by microbes, algae, and plants. The risks of chemicals, such as pesticides, whose use is determined by population responses of fungi, weeds, and lower-order animals, or those, like mercury, whose speciation is altered by the activity of micro-organisms, will also be significantly affected. While the absolute magnitude of changes in average air concentrations related to GCC may be relatively small for a given air pollutant, widespread human exposures, increased peak concentrations in certain geographical areas, and significant health consequences make such impacts of GCC very important from a public-health standpoint.

These alterations in risks have implications for national and international decision makers involved in the regulation and authorization of chemical products and the monitoring and management of chemicals in environmental matrices and foodstuffs. The expected changes reveal that some of the scenarios and models currently used in health risk assessment of chemicals will need updates and revision in order to reflect some of the future changes described earlier. Monitoring methodologies may also need to be adapted in order to cope with increased variability in exposure, sensitivity, and risk, both spatially and temporally. Monitoring and sampling should be done at a frequency sufficient to capture variability, which is likely to increase in many places.

It is also important to recognize that human exposure to chemicals in the environment in the future will be affected by other, non-climate-related drivers such as increased urbanization, future technological developments (such as a move toward more environmentally benign pesticides), ongoing strategies to reduce emissions and other environmental releases (e.g., of persistent organic pollutants), and economic changes. In some cases, these drivers may have a bigger impact on human exposure (either increasing or lowering exposures) and risks than GCC alone.

There are, however, major gaps in our current understanding of how chemical risks will change. A concerted effort is therefore needed at an international level to better characterize the potential impacts of GCC and other future drivers on exposure, sensitivity, and risk. We recommend that work should focus on the following areas. First, the development of future models and scenarios of land use and social, technological, and economic change in order to provide a basis for informing how inputs of chemicals to the environment, in different regions of the world, may change in the future. Second, work should focus on the generation of improved data sets and models for determining future human exposure to chemicals in different environmental matrices. This work should consider the importance of emerging exposure pathways, such as increased inhalation of contaminated dust or exposure consequences of flooding, and consider the implications of human behavioral change on the degree of exposure. Furthermore, there should be focus the development of research programs that aim to fill gaps in our understanding of the interactions between climate and weather parameters and human sensitivity to chemical exposures. Focus should also be given to the refinement of regulatory models and procedures in the light of knowledge gained from work on exposure and human sensitivity to toxicants. Existing risk assessments and chemical management programs should also be updated to determine whether the risks of a current-use product could change in the future. Finally, work should give focus to the development of targeted surveillance schemes for the presence and health effects of select chemicals in different environmental compartments for different regions of the world and at smaller geographical scales to address inequities at the community level.

To address these knowledge gaps, input is required from a wide range of disciplines (including climate science, toxicology, exposure science, public health, environmental modeling, social science, economics, and environmental chemistry) and a range of sectors across the globe. It is essential that future research and assessment programs take a holistic approach and do not just focus on GCC-driven changes alone. Research programs should also include elements of technology transfer and capacity building for developing countries struggling to adapt to GCC impacts, many of which will be most vulnerable to the forecast changes in chemical exposure. Figure 4 below shows the conclusive working model envisaged in this review paper.

GCC Alterations in Chemical fate and Transport

Increased temperatures can increase metabolic rates for many organisms, thereby increasing the potential for bioaccumulation and biomagnification of some contaminants. Temperature-related increases in the uptake and bioaccumulation of metals have been reported for several marine organisms, including crustaceans, echinoderms, and mollusks. In a recent modeling exercise of the uptake of methylmercury, increases in temperature resulted in increased concentrations of the compound in fish and mammals; temperature increases would also be expected to accelerate the conversion of mercury to methylmercury. In some instances, uptake may decrease. Studies of organochlorine concentrations in fish between 1994 and 2008 showed a decline in concentrations with increasing temperature, a trend that could be explained by declines in lipid content over time. The reason for the change in lipid content and a possible association with climate effects are unclear.

Acknowledgments

I shall be remiss without appreciating the work of Prof. Shem Wandiga, Prof.  Dan Olago and Prof.  Nicholas Oguge of the Institute of Climate Change and Adaptation (ICCA), University of Nairobi for mentoring, teaching and supervising my Doctoral Research. My research work was entitled Vulnerability Assessment of Terrestrial Large Mammals as Indicators Species to Climate Change in Mt. Elgon National Park, Kenya. The Professors demonstrated profound knowledge and understanding of the concepts and complexities encapsulate in the study of Global climate change.

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