The impact is agriculture and ecosystem collapse, it risks extinction

Volume 156, November 2021, Science Direct, //DH

Rockström et al. (2009) warned that chemical pollution is one of the planetary boundaries that ought not to be crossed to safeguard humanity. Altogether more than nine million humans are dying prematurely each year – one in six deaths – due to contamination of their air, water, food, homes, workplaces, or consumer goods (Landrigan et al. 2018). To place this in perspective, the chemical-related annual death toll is significantly greater than that of World War II and today constitutes the greatest preventable form of mortality. Furthermore, it inflicts catastrophic losses on wildlife, notably insects and animals that depend on them, ecosystems and their services, such as pollination or clean water, on which humans depend for our own existence. This underlines the role of chemical pollution in potential planet-wide ecological breakdown (Dave 2013). There is increasing evidence in recent decades of cognitive, reproductive and developmental disorders and premature deaths caused by chemical contamination of the human living environment (Diamanti-Kandarakis et al. 2009).

Food can be contaminated at several stages before consumption - during crop or forage or animal production and harvesting, or post-harvest during storage, processing, transport and processing. Heavy metal(loid)s, pesticides, dioxin, PCBs, antibiotics, growth-promoting substances, packaging residues, preservatives and excess nutrients (e.g. nitrate) have all been found to contaminate food at higher than acceptable levels (Awata et al., 2017, EFSA, 2018, Islam et al., 2017, Licata et al., 2004). This affects vegetables, grains, fish, and livestock via soil, surface water, groundwater or aerial deposition (Zhong et al. 2015) (Fig. 3). For example, Cd concentrations of various foodstuffs in China, including vegetables, rice, and seafood, were as high as 0.93 mg/kg and contributed 1.007 µg/kg bodyweight to the daily intake for children, which is 1.2 times higher than the acceptable limit recommended by WHO and the FAO (Zhong et al. 2015). Dioxin and PCB-like contaminants in food are also a concern to human health according to a report commissioned by the European Food Safety Authority (EFSA). Similarly, human exposure to pesticides can occur from residues in food or from legacy or inadvertent contamination during production and processing. Such contamination of food products can have chronic impacts on human health (The Gurdian 2004). A recent study of pesticide pollution at global scale reported that 64% of agricultural land was at risk of pollution caused by multiple active ingredients of pesticides. The risk includes adverse effects on food and water quality, biodiversity and human health (Tang et al. 2021).

Post-harvest protection of food can also result in contamination by fumigants, formalin and other insecticides and preservatives (e.g. calcium carbide, cyanide, sodium cyclamate, urea, melamine, aflatoxin and detergents), especially when they are used incorrectly, illegally or accidentally. Serious examples have been reported from numerous countries, including China, India, and Brazil (Handford et al. 2016). Even in countries with well-defined and established regulatory systems, such as those of the EU, chemical contamination in food and animal feed can occur to an extent sufficient to cause concern, due to intentional and unintentional use of post-harvest chemicals (Silano and Silano 2017).

6.2. Loss of soil productivity

Healthy soils are essential for safe, healthy food, ecosystem service delivery, climate change abatement, abundant food and fibre production, pollutant attenuation and freshwater storage, all of which are key to the sustainability of the world food supply. Reduced food availability and security in less-developed countries can occur when productive land is lost due to chemical contamination (Fig. 3). In the last 40 years nearly one-third of the Earth’s total arable land has been lost to soil erosion, desertification, urban expansion, and contamination (Cameron et al. 2015). Soils contaminated with heavy metals and pesticides cause loss of productive agricultural land and compromise food production and quality (Fig. 3). There is no global estimate of the areal losses of arable land attributed to chemical pollution, but regional reports indicate significant loss or potential loss. For example in Europe, 137,000 km2 of agricultural lands are at risk of being abandoned due to heavy metal(loid)s pollution (Tóth et al. 2016). This situation is exacerbated in developing countries by inadequate waste treatment and uncontrolled exploitation of natural resources (Lu et al., 2015, Tóth et al., 2016). China lost 0.13% of its total arable land due to chromium (Cr) pollution during 2005–2013 and 1.3% remains at risk (Lu et al., 2015, Tóth et al., 2016). Yet, key policy instruments and initiatives for sustainable development rarely recognise that contaminated soils compromise food and water security.

6.3. Biodiversity loss and damage to crops and livestock

Biodiversity in the Earth’s surface layer from bedrock to the vegetation canopy provides the primary source of services for the support of life on Earth (Banwart et al. 2019; Cardinale et al. 2012). The acute and chronic impact of excessive current and historical use of agrichemicals and other industrial pollutants is contributing to a substantial loss of Earth’s biodiversity. The global loss of honeybee communities due to neonicotinoid pesticides has caused an international crisis for crop pollination (Dave 2013), for example. There are reports of pesticide pollutants causing the loss of more than 40% of the total taxonomic pools of stream invertebrates in some regions (Beketov et al. 2013). Residues of more persistent chemicals, including many pesticides, may have long-term ecological impacts, especially in highly contaminated areas (Gevao et al. 2000) with significant threats of pollution of groundwater and marine water (Arias-Estévez et al., 2008, Jamieson et al., 2017). Losses of up to 78% of insect species have been reported from 290 sites in Germany (Seibold et al. 2019). Such ecological impacts and their persistence may profoundly alter biological processes such as decomposition and soil formation in natural environments, leading to unfavourable or challenging settings for human food production.

Reactive nitrogen pollution of the atmosphere and its deposition are responsible for declining biodiversity at regional (Hernández et al. 2016) and global scales (Condé et al. 2015). For example, assessing more than 15,000 sites, including forest, shrubland, woodland and grassland in the USA, Simkin et al. (2016) found that 24% of the sites had losses of vulnerability of species as a result of atmospheric nitrogen deposition, in particular when the disposition was above 8.7 kg N/ha/yr. A similar study in the UK also revealed that species richness had declined with increases of nitrogen deposition in the range of 5.9 to 32.4 kg N/ha/yr (Southon et al. 2013). Excess loading of nutrient pollutants by human activities affects hundreds of coastal and marine ecosystems and has been linked to a ‘missing’ biomass of flora and fauna (Diaz and Rosenberg 2008).

At a global scale there is also evidence that low crop yields may be caused by surface (tropospheric) ozone (O3) pollution (Tai et al. 2014); elevated O3 levels are also linked to chemical pollutants. It was projected that by 2030 that O3 precursors could cause crop yield losses for wheat (4–26%), soybeans (9.5–19%) and maize (2.5–8.7%) globally (Avnery et al. 2011). Reduction of crop yield due to the O3 exposure has also been reported by several regional experimental and model studies (Debaje, 2014, Hollaway et al., 2012, Kumari et al., 2020). The yield losses occur as a result of plant physiological interference with the O3 molecules such as the production of reactive oxygen species mainly through the diffusion of O3 into the intercellular air space of plant leaves (Ainsworth 2017).

7. The chemical pollutant challenge for humanity: Discussion and questions

From a toxicological point of view, exposure to the vast array of modern chemicals and their billions of mixtures might cause acute or chronic toxicity but also not pose any toxic risk to humans. This wide range of threats can be addressed using a risk-based approach (Siegrist and Bearth 2019). Due to methodological constraints and the varying susceptibility to toxins among humans, there are only a few reports showing direct quantitative, whole life-span analyses of fatalities attributed to environmental pollutants (section 2–6). Nevertheless, compilation of the substantial evidence of the health burden caused by chemical pollution both show and predict the impairment of normal human life expectancy by direct exposure to pollutants, food contamination and fertility decline (Fig. 4) (Aitken et al., 2004, Hou and Ok, 2019, Rabl, 2006).

Rockström et al. (2009) described nine planetary boundaries that humans ought not to breach for our own safety: climate change, ocean acidification, stratospheric ozone, global phosphorus and nitrogen cycles, atmospheric aerosol loading, freshwater use, land-use change, biodiversity loss, and chemical pollution. Later, ‘chemical pollution’ was not considered as a single entry (Condé et al. 2015) as they also cause climate change (e.g. emissions of CO2, methane and other greenhouse gases), ocean acidification due to elevated CO2, depletion of stratospheric ozone due to released halocarbons, and interruption of P and N cycles. As pointed out here, atmospheric aerosol loading is another aspect of anthropogenic chemical pollution (Singh et al. 2017), and ambient air pollutants are responsible for millions of premature deaths and cost many billions of dollars (West et al. 2016).

Every year thousands of new chemicals are produced and most of them remain beyond current risk assessment regulations (Sala and Goralczyk, 2013, Wang et al., 2020). The effects of mixed pollutants are especially unclear (Heys et al., 2016, Konkel, 2017). This due to inadequate methodology to assess the interaction of chemical mixtures and the risk factors for human health (Heys et al. 2016), although the effects of mixed pollutants on human health are probably physiologically more relevant than that of any single pollutant (Carpenter David et al. 2002). Global climate change, including warming and extreme climatic conditions, will exacerbate human exposure to chemical pollutants present in soil and water (Biswas et al. 2018). Erosion and aerial transport of polluted soil or acidification of soil and water causing mobilisation of toxic heavy metal(loid)s are two mechanisms by which this can occur. There is in general far too long a delay between scientific discovery of pollution problems and their effects, and regulations and actions to abate them.

It is likely humanity is approaching a dangerous tipping point due to our release of geogenic, anthropogenic synthetic chemicals (Table 1, Table 2 and SI Box S1). This raises the issue that, as yet, no scientifically credible estimate has been made of humanity’s combined chemical impact on the Earth and on human health. This gap was highlighted by Rockström et al. (2009) whose popular ‘global boundaries’ chart was unable to include a boundary for chemical emissions because of a lack of data and suitable methodology. Public awareness is constrained by several issues, including the fact that toxic chemicals are now so widely dispersed throughout the Earth’s biosphere that their origins are untraceable, that cases of poisoning may take decades to be officially noticed, researched and proven, that the polluters may not be aware of or well-equipped to curb the pollution, that consumers and many professionals may be insufficiently educated in the risks. There are several local incidents that the aftermath analysis could reveal the insufficiency of knowledge regarding the effect of synthetic chemicals. For instance, the Bhopal Union Carbide gas disaster of 1984 of such categories where gaseous contaminant levels were so high that people died immediately following exposure.

Consequently, humanity is unaware of how near or far it is from exceeding the Earth’s capacity to ‘absorb’ or safely process our total chemical releases, which grows by many billions of tonnes with each passing year. This represents a potential catastrophic risk to the human future and merits global scientific scrutiny on the same scale and urgency as the effort devoted to climate change.