Environmental Toxicology: A historical overview since ‘Silent Spring’

Have the harmful effects of chemicals upon man and ecosystems lessened since Rachel Carson published her book ‘Silent Spring‘ in 1962?

A derelict, silent world where birds do not sing, chicks do not hatch, dead vegetation dominates the landscape and illness of men, women and children has prevailed. The opening fable of Rachel Carson’s book ‘Silent Spring’ depicts a world that has been ravaged by the widespread use of harmful pesticides. Described in her own words as, “A spring without voices”, (Carson, 1962). Now recognised as one of the most influential and controversial books of the twentieth century, it ignited the environmental movement by highlighting the adverse environmental and health impacts of pesticides. 

Rachel Carson bravely accused the chemical industry of spreading, what we would call today, ‘fake news’. Information to deliberately deceive the masses. This of course, caused uproar to anyone with a vested interest in making money from pesticides and chemicals. Although engulfed in backlash and controversy, it also paved the way for major federal reforms in the USA.

Back in 1913, Fritz Haber, a German Chemist, was well underway with manufacturing nitrogenous fertilisers by synthesising ammonia from nitrogen gas. The agricultural revolution saw a huge rise in the use of biocidal agents such as pesticides and herbicides, but nobody knew at this time, the impact they would inflict upon the environment and people.

Sixty years on from ‘Silent Spring’, have environmental issues grown larger or are we just increasingly aware of them the more urgent they become? This article seeks to explore if the harmful effects of chemicals such as pesticides and heavy metals, have lessened since Rachel Carson published her influential book by journeying through a timeline of notable events in the world of environmental toxicology.

In the run up to ‘Silent Spring’, synthetic pesticides had already been distributed so widely and frequently that they existed pretty much everywhere, (Carson, 1962). The issue with such chemicals is that they persist in soil and contaminate water systems, giving them the name persistent organic pollutants (POPs). They embed themselves in the bodies of wildlife, bio-accumulating and slowly making their way up the food chain. Synthetic pesticides have been found in fish that swim in the remotest of lakes, earthworms that burrow the soils and even in humans, (Carson, 1962). Nothing can escape. In the initial wake of ‘Silent Spring’, people started talking. People started to take notice of the environment around them. Big policy changes were about to happen and the environmental movement was set in motion. 

In 1965, The International Agency for Research on Cancer (IARC) was founded. It was known by this point that Cancer, a form of chronic toxicity, was caused by repeated exposure to some chemicals for long periods of time, (ATSDR, n.d). By categorizing and evaluating chemicals, the IARC allowed people to gain information on the known or suspected carcinogens to humans and that in turn allowed people to minimise their risk of coming into contact with such substances, thus reducing cancer, shown in below:

GroupWhat does it mean?What does it include?
1Carcinogenic to humansSmoking, UV radiation, alcohol, processed meats
2AProbably carcinogenic to humansFrying, steroids, exposures from working in hair dressing, red meat
2BPossibly carcinogenic to humansCoffee, gasoline, exhaust fumes, pickled vegetables
3Carcinogenicity not classifiableTea, static magnetic fields, flourescent lighting, polyethene
4Probably not carcinogenicOnle 1 chemical ever placed in this group

IARC Carcinogen Classification. Adapted from Compoundchem.com (2015)

An oil spill in Santa Barbara, 1969, heightened concerns about water pollution when gallons of oil engulfed beaches from an offshore oil rig disaster. Efforts to contain the oil spill were unsuccessful and sadly, no surfactant existed back in 1969 to remove the oil from the birds it chocked, without removing the birds essential oil (Sabol Spezio, 2018). Many marine animals perished. 10,000 tons of oil, a natural occurring hydrocarbon organic compound, spilled into the ocean and over 2,200 birds were recovered, none of which were released despite rehabilitation attempts (Newman et al., 2002). When spilled into the sea, UV radiation from the sun sets of a photolysis reaction, oxidizing some of the components of oil into acidic and phenolic compounds which are thought to be more toxic than the original hydrocarbons, (Kingston 2002). Hydrocarbon toxicity is also the cause of approximately 20 human deaths per year in the USA, (Brown and Armstrong, 2021).

In the same year, Under Secretary of the Interior, Russell Train said during the Centennial of the American Museum of Natural History, “If environmental deterioration is permitted to continue and increase at present rates, [man] wouldn’t stand a snowball’s chance in hell [of surviving]”, (Lewis, 1985). This highlighted the increasing awareness of the links between environmental damage and human health. The Santa Barbara oil disaster highlighted the lack of environmental policy in the USA and The National Environmental Policy Act of 1970 (NEPA) was born, (Sabol Spezio, 2018). Citizens now had a voice and a place at the table, unlike the residents of Santa Barbara, in 1969.

Growing pressures on the US Nixon administration led to a groundbreaking environmental action plan to improve water and air quality. This was the start of the US Environmental Protection Agency (EPA) in 1970. By the 1970’s, almost all petrol produced around the world contained lead, a toxin to multiple human organs, (Landrigan, 2002). One of the points proposed by Nixon was to tax lead additives in petrol and included approval of a contingency plan against oil spills. The first ever Earth Day was celebrated shortly after the EPA introduction, in April 1970, marking the anniversary of the birth of the modern environmental movement and is still celebrated today.

Although a step in the right direction, there were still a lot of unknowns at this point. The Vietnam war, between 1961 and 1971, saw more than 91 million liters of Agent Orange, a herbicide, dumped onto South Vietnam by US forces, having detrimental effects to both human health and the environment. In an attempt to control the undergrowth vegetation, Agent Orange defoliated around 3.1 million hectares of tropical biodiverse rainforest and mangroves leaving high levels of dioxin in the soil, water and sediments, (Truong and Dinh, 2021). Many early studies were carried out into the effects of Agent Orange, including one by the Bionetic Research Laboratories in 1965. They found malformations in test animals were caused by 2,4,5-T, a component of Agent Orange, (Institute of Medicine, 1994). The use of Agent Orange was eventually suspended, on April 15, 1970 (Hynes, 2016). There is now sufficient evidence of an association between Agent Orange and some types of cancers and birth defects, (Frumkin, 2003). Many lawsuits were filed on behalf of both U.S. and Vietnamese veterans who sought compensation for damages due to being exposed to Agent Orange. The Agent Orange Act, 1991 was introduced to establish and summarise the scientific evidence regarding exposure to defoliants, dioxins and herbicides during the Vietnam War.

The 70’s, saw the introduction of the Clean Air Act, 1970. The law set statutory deadlines for reducing pollution caused by road traffic emission levels. It set specific standards such as the 8-h standard of 140 micrograms/cubic meter for ozone, (Sabio Spezio, 2018). Chay and Greenstone (2003), stated that air quality in the USA improved dramatically in the 1970s and 1980s, with particulate concentrations falling from an average of 95 micrograms-per-cubic meter (µg/m3) to about 60 µg/m3. Their research found that roughly 1,300 fewer infants died in 1972 than they would have in the absence of the Clean Air Act. It got off to a good start however, a recent report from the Congressional Research Service, admits that statutory deadlines to control emissions have often been missed as a result of delayed standard-setting by EPA, delayed action on implementation by states and local governments, or law suits, (Congressional Research Service, 2022). The age old saying, better late than never springs to mind here though.

The 70’s also saw one of the most notable changes to come out of ‘Silent Spring’. The banning of the now infamous pesticide known as DDT (Dichlorodiphenyltrichloroethane), in the USA in 1972. The bee killer! By this time the rippling environmental movement was catching on globally. Although more than ten years later, the UK finally caught up, banning DDT in the 1980s. Ecuador, Mexico and Venezuela phased it out in 2000, (Van den Berg, 2009).

Over the years, the use of DDT for malaria control has caused a bit of a stir and debates have become heated. On one side, the World Health Organisation (WHO) openly endorses the use of DDT as a useful insecticide for malaria control, (Schapira, 2006), on the basis that it saves millions of lives. An extremely valid argument. DDT clearly has its benefits, however it is also a persistent organic pollutant, meaning it lingers in the environment for long periods of time. Due to their volatility, ubiquity, lipophilicity and ability to bioaccumulate in different matrixes causing chronic toxicity, POPs are of high global concern, (Villaba, et.al., 2020). A study into the effects of POPs, OCPs, PCBs and PBDEs and chlorophyrifos on honey bees, concluded that despite worldwide bans on most of the compounds, their residues are still present in a variety of matrices both biotic and abiotic, which threatens the sustainability of beehives, (Villaba, et.al., 2020). DDT has also been linked to issues with human health, with a study conducted by La Merrill, et.al (2020), concluding that DDT exposure is significantly associated with increased obesity risk.

But what are the alternatives? Organophosphates replaced organochlorides such as DDT and are generally considered safe to use on crops, however OPs are mutagenic and teratogenic and diseases of the nervous and immune system of mammals can be linked to these pesticides, (Ragnarsdottir, 2000). There are chemical, biological, physical/mechanical and cultural alternatives but they all come with their own limitations, (Hossain et al., 2017). 

By the 1980’s, increased anthropogenic activity was altering marine and terrestrial environments worldwide. The nuclear disaster of Chernobyl, Ukraine, in April 1986 has since rendered the Baltic Sea one of the most polluted bodies of water in the world, (Kotilainen et al., 2021). The culprit; 137Cs (Caesium) radionuclide, a heavy alkali metal, with a half-life of around 30.05 years. The below image shows the scale of terrestrial 137Cs contamination as a result of the Chernobyl fall out, with the greatest deposition occurring in areas surrounding the Gulf of Bothnia and the Gulf of Finland, (Kotilainen et al., 2021).

Terrestrial deposition of Chernobyl-derived 137Cs in the Baltic Sea drainage area (kBq m−2). (Kotilainen et al., 2021).

Chernobyl is still to this day considered the worst nuclear disaster ever, exposing thousands of people to high levels of radiation. Cardis et al., (2006) estimated that Chernobyl may have caused around 1,000 cases of thyroid cancer and 4,000 cases of other cancers in Europe. Rumors and conspiracies circulated and people were seeking the truth. The United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) 2000 Report, summarising the effects of the Chernobyl disaster, came to the following conclusion; Reports of health effects caused by radiation have been greatly exaggerated and there is no scientific evidence of an increase in overall cancer incidence or mortality that could be associated with radiation exposure, (Rahu, 2003). Some say the report dispelled myths, others claim that it supported atomic lobby interests, (Rahu, 2003).

In the months following the Chernobyl disaster, two global agreements relating to nuclear safety were adopted. The Convention on Early Notification of a Nuclear Accident and the Convention on Assistance in the Case of a Nuclear Accident or Radiological Emergency, both of which have significantly strengthened the global nuclear safety regime, (Dixit, 2016). Ten years later, in 1996, the Convention on Nuclear Safety also came into force, further strengthening nuclear safety legislation.

The end of the 1980’s saw another oil rig disaster on an even greater scale. 11 million tonnes of oil spilled into the ocean from the Exxon Valdez ship after it hit a reef. In response, congress passed the Oil Pollution Act of 1990, which stated that companies responsible for such oil tanker spills were ultimately responsible for cleaning it up, remediating damage and the costs associated with it, (LeVine, 2019).

The 90’s saw Erin Brockovich come to prominence in 1993, when she publicised the water crisis in California. A Group 1 IARC carcinogen, Chromium, had leaked into the drinking water supply. Heavy metals, such as Chromium, Arsenic and Lead, are toxic and have multiple applications including anthropogenic sources such as mining, agriculture and industrial waste and also natural sources such as volcanic eruptions, (Sharma et al., 2021). Sharma et al., (2021) concluded that heavy metals are not able to be removed from the environment entirely however, they can be broken down and converted to lesser toxic forms and suggests further research is needed into elimination removal techniques.

Image found on Frontiers

The noughties saw yet another major oil spill disaster at the Deepwater Horizon offshore oil rig in 2010. A series of deficiencies were identified and exposed in the disaster by the companies governing the operations. Surprisingly at the time, congress did nothing to address these, (LeVine, 2019). Barak Obama, the President at the time, stepped in and created the National Commission on the BP Deepwater Horizon Oil Spill and Offshore Drilling, in an attempt to help prevent a disaster like the Deepwater Horizon happening again, (LeVine, 2019). Were things finally changing? Needless to say there hasn’t been another major oil spill event since. Yet!

Both POPs and heavy metals were gaining attention throughout the noughties. In May 2004, The Stockholm Convention came into force. Its main objective was to protect human health and the environment from persistent organic pollutants by prohibiting and or eliminating its use and is considered a success (UNEP, 2010). The Minamata Convention on Mercury followed in 2013, that aims to protect human health from toxic Mercury containing compounds. It was released as a result of industrial activities resulting in methyl mercury in wastewater systems contaminating marine life, (Mercury Convention, 2019). 

Over the past 60 years since ‘Silent Spring’ was thrust into the public eye, many policy changes have occurred in the world of environmental toxicology. From new organizations such as the EPA being formed, toxic chemicals such as DDT being banned across the globe to POPs being prohibited and banned under the Stockholm Convention. These legislations have come about as our knowledge and awareness of these chemicals has increased. ‘Silent Spring’ helped to inspire an environmental movement that is still ongoing today. Whether it’s water, air or soil contaminants we are far more aware of the ecological interactions with chemicals.

In the case of cancer causing chemicals, the effects of chemicals upon man have most certainly lessened since ‘Silent Spring.’ We as humans, are far more aware of the carcinogenic effect of chemicals thanks to the IARC classifications, meaning we are able to avoid or limit our exposure to carcinogens. The research by Chay and Greenstone concluded that far more infants would have died should the Clean Air Act not have been bought in to force. It’s there in the science, in black and white.

Although she was not alone in sounding the alarm, if Rachel Carson had not published her book there would have evidently been a delay in the realisation and recognition of the harmful effects of pesticides and other POPs on the environment and humans. We know that POPs bioaccumulate over time. Did Rachel raise the alarm at just at the right time? What further damage could have been done if she had not? We may never know the answers to these questions in full, but we can assume that the effects of chemicals on man and ecosystems have lessened since she published ‘Silent Spring’.

Silent Spring,1962


ATSDR (n.d) Chemicals, ‘Cancer and You’, Agency for Toxic Substances and Disease Registry [Online]. Available at: https://www.atsdr.cdc.gov/emes/public/docs/Chemicals,%20Cancer,%20and%20You%20FS.pdf (Accessed 05 March 2022).

Brown, W.K. and Armstrong, T.J. (2021) ‘Hydrocarbon Inhalation’ StatPearls [Online]. Treasure Island (FL): StatPearls Publishing; 2022 Jan, Available at: https://www.ncbi.nlm.nih.gov/books/NBK470289/ (Accessed 20 February 2022).

Cardis, E., Krewski, D., Boniol, M., Drozdovitch, V., … (2003) ‘Estimates of the Cancer Burden in Europe From Radioactive the Fallout From the Chernobyl Accident’, International Journal of Caner, 119(6), pp. 1224-1235, doi; 10.1002/ijc.22037 (Accessed 20 February 2022).

Carson, R. (1962) Silent Spring. London: Penguin Books.

Chay, K.Y., Greenstone, M. (2003) ‘Air quality Infant Mortality and the Clean Air Act of 1970’, National Bureau of Economic Research, 10053, doi: 10.3386/w10053 (Accessed 20 February 2022). 

Compoundchem (2015) A Rough Guide to the IARC’s Carcinogen Classifications. [Online]. Available at: https://www.compoundchem.com/2015/10/26/carcinogens/ (Accessed 05 March 2022). 

Congressional Research Service (2022) ‘Congressional Air Act: A Summary of the Act and Its Major Requirements’, Congressional Research Service [Online]. Available at https://sgp.fas.org/crs/misc/RL30853.pdf (Accessed 26 February 2022).

Dixit, A. (2016) ‘30 Years after Chenobyl: IAEA Continues to Support Global Efforts to Help Affected Regions’, International Atomic Energy Agency, [Online]. Available at https://www.iaea.org/newscenter/news/30-years-after-chernobyl-iaea-continues-to-support-global-efforts-to-help-affected-regions (Accessed 20 February 2022).

Frumkin, H. (2003) ‘Agent Orange and Cancer: An Overview for Clinicians’, CA: A Cancer Journal for Clinicians, 53(4), pp. 245-255, doi: 10.3322/canjclin.53.4.245 (Accessed 27 February 2022).

Hossain, L., Rahman, R., Khan, M.S. (2017) ‘Alternatives to Pesticides’, Pesticide Residue in Food, pp. 147-165, doi: 10.1007/978-3-319-52683-6_9 (Accessed 27 February 2022).

Hynes, P.H (2016) ‘The Legacy of Agent Orange in Vietnam’, Peace Review, 28(1), pp. 114-122, doi: 10.1080/10402659.2016.1130415 (Accessed 05 March 2022).

Institute of Medicine (US) Committee to Review the Health Effects in Vietnam (1994) ‘Veterans of Exposure to Herbicides’, Veterans and Agent Orange: Health Effects of Herbicides Used in Vietnam. Washington (DC): National Academics Press (US).

Kingston, P.F. (2002) ‘Long-term Environmental Impact of Oil Spills’, Spill Science & Technology Bulletin, 7(1-2), pp. 53-61, doi: 10.1016/S1353-2561(02)00051-8 (Accessed 20 February 2022).

Kotilainen, A.T., Kotilainen, M.M.m Vartti, V.P., Virtasalo, J.J. (2021) ‘Chernobyl Still with Us: 137Caesiu, Activity Contents in Seabed Sediment from the Gulf of Bothnia, Northern Baltic Sea’, Marine Pollution Bulletin, 172(112924), doi: 10.1016/j.marpolbul.2021.112924 (Accessed 20 February 2022).

La Merrill, M.A., Krigbaum, N.Y., Cirill, P.M., Cohn, B.A. (2020) ‘Association Between Maternal Exposure to the Pesticide dichlorodiphenyltrichloroethane (DDT) and Risk of Obesity in Middle Age’, International Journal of Obesity, 44(1723-1732), doi: 10.1038/s41366-020-0586-7 (Accessed 26 February 2022).

Landrigan, P.J (2002) ‘The Worldwide Problem of Lead in Petrol’, Bulletin of the World Health Organisation, 80(10), [Online]. Available at https://www.who.int/bulletin/archives/80(10)768.pdf (Accessed 26 February 2022). 

LeVine, M. (2019) ‘What Have We Learned from 50 Years of Offshore Oil Disasters’, Ocean Conservancy [Online]. Available at https://oceanconservancy.org/blog/2019/02/05/learned-50-years-offshore-oil-disasters/ (Accessed 20 February 2022).

Lewis, J. (1985), ‘The Birth of EPA’, US Environmental Protection Agency, [Online]. Available at: https://archive.epa.gov/epa/aboutepa/birth-epa.html (Accessed 19 Feb 2022).

Mercury Convention (2019) ‘Minamata Convention on Mercury’ United Nations Environment Programme [Online]. Available at: https://www.mercuryconvention.org/sites/default/files/documents/information_document/Minamata-Convention-booklet-Sep2019-EN.pdf (Accessed 05 May 2022).

Newman, S.H., Ziccardi, M.H., Berkner, A.B., Holcomb, J., Clumpner, C., Mazet., J.A.K. (2002) ‘A Historical Account of Oiled Wildlife Care in California’, Marine Ornithogy, 31, PP.59-64, [Online]. Available from: http://www.marineornithology.org/content/get.cgi?rn=558 (Accessed 20 February 2022).

Ragnarsdottir, K.V (2000) ‘Environmental Fate and Toxicology of Organophosphate Pesticides’, Journal of The Geological Society, 157(4), pp. 859-876, doi: 10.1144/jgs.157.4.859 (Accessed 27 February 2022).

Rahu, M. (2003) ‘Health Effects of the Chernobyl Accident: Fears, Rumours and the Truth’, European Journal of Cancer, 39(3), pp. 295-299, doi: 10.1016/S0959-8049(02)00764-5 (Accessed 20 February 2022).

Schapira, A. (2006) ‘DDT: A Polluted Debate in Malaria Control’, The Lancet, 368(9553), pp. 2111-2113, doi: 10.1016/S0140-6736(06)69812-7 (Accessed 26 February 2022).

Sharma, N., Sodhi, K.K., Kumar, M., Singh, D.K. (2021) ‘Heavy Metal Pollution: Insights Into Chromium Eco-Toxicity and Recent Advancement in its Remediation’, Environmental Nanotechnology, Monitoring & Management, 15, doi: 10.1016/j.enmm.2020.100388 (Accessed 26 February 2022).

Spezio, T.S. (2018) ‘The Santa Barbara Oil Spill and its Effect on United States Environmental Policy’, Sustainability, 10(8), 2750, doi: 10.3390/su10082750 (Accessed 20 February 2022).

Truong, K.N., Dinh, K.V. (2021) ‘Agent Orange: Haft-Century Effects on the Vietnamese Wildlife Have Been Ignored’, Environmental Science and Technology, 55(22), 15007-15009, doi: 10.1021/acs.est.1c06613 (Accessed 26 February 2022).

UNEP (2010) ‘Riding the World of POPs: A Guide to the Stockholm Convention on Persistent Organic Pollutants’, United Nations Environment Programme [Online]. Available at: http://chm.pops.int/Portals/0/sc10/files/c/ridding_the_world_of_pops_e.pdf (Accessed 26 February 2022).

Van den Berg, H. (2009) ‘Global Status of DDT and its Alternatives for use in Vector Control to Prevent Disease’, Environmental Health Perspect, 117(11),1656-1663 doi: 10.1289/ehp.0900785 (Accessed 19 February 2022).

Villaba, A., Maggi, M., Ondarza, P.M., Szawarski, N., Miglioranza, K.S.B. (2020) ‘Influence of Land Use on Chlorpyrifos and Persistent Organic Pollutant Levels in Honey Bees, Bee Bread and Honey: Beehive Expose Assessment’, Science of the Total Environment, 713, doi: 10.1016/j.scitotenv.2020.136554 (Accessed 26 February 2022).

Visme (2022) Infographic Templates. Available at: https://www.visme.co/ (Accessed 26 February 2022).

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s