The legacy of Rachel Carson
Meeting report by Kate Jones and James Lymer
Secretary of the Toxicology Group and the ECG
ECG Bulletin February 2013
Secretary of the Toxicology Group and the ECG
ECG Bulletin February 2013
A report of the meeting to commemorate the 50th anniversary of Silent Spring held at the RSC’s Chemistry Centre in London on 2 October 2012. This joint meeting was organised by the RSC Toxicology Group and the RSC Environmental Chemistry Group together with The Institution for Environmental Sciences, and was supported by the RSC’s Environment, Sustainability and Energy Division.
The aim of the meeting was to present a number of perspectives on how Rachel Carson’s work contributed to the legislative, chemical and societal world we see today. Copies of the presentations from the speakers are available from the ECG website (www.rsc.org/ecg).
The aim of the meeting was to present a number of perspectives on how Rachel Carson’s work contributed to the legislative, chemical and societal world we see today. Copies of the presentations from the speakers are available from the ECG website (www.rsc.org/ecg).
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The meeting began with Professor Andy Smith (MRC, Leicester) giving a brief history of Rachel Carson’s work. Amongst other details, he highlighted the difficulties of being a female scientist at that time. Carson first published on the environment in 1941 in her book Under the Sea-wind – recently republished by Penguin Classics, but it was not until her 1951 book The Sea Around Us (which won many prizes, and is also in print), that she attracted widespread public attention. She then became increasingly concerned with the effects of extensive pesticide use, culminating in the publication of Silent Spring in 1962. For the views expressed in this book, she was attacked by the chemical industry and even by the U.S. Department of Agriculture but was backed by President Kennedy’s Scientific Advisory Committee in her findings. By this time, Carson was in poor health. She died in 1964, thus undoubtedly cutting short her contribution to the field.
One of the chemicals identified by Carson in Silent Spring was DDT. Professor Smith went on to give an overview of DDT use and toxicity. Prior to DDT, alternatives were either ineffective (e.g. pyrethrins) or highly toxic (e.g. arsenicals). |
Neftali/Shutterstock
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DDT was first discovered in 1874 but it was not until 1939 that Paul Müller (Geigy, Basle) found that it was highly effective in killing insects. During the Second World War, DDT was a vital addition to the armoury in defeating malaria and typhus ‒ diseases that could cause as many casualties as war itself. This fast-track use led to Müller being awarded the Nobel Prize in 1948. After the Second World War, the use of DDT escalated, and it was used as a widespread general-purpose insecticide in agriculture. The problems of DDT seemed to stem from overenthusiastic use with little concern for long-term consequences. With respect to human health effects, Carson was most concerned with cancer. DDT is slowly metabolised, with high doses causing tremors in humans, but it is a poor mutagen. To date there is weak evidence for DDT being associated with either liver or breast cancers, indicating that the threshold for any effects is far above current, and even historic, exposure levels. Most concern these days is with its potential reproductive effects as an oestrogen mimic.
Following Carson’s work, DDT was banned in the US in 1972. Over the following decades, many countries across the globe followed suit, although some use continues today for indoor residual spraying to control malaria. However, even here there is ongoing controversy as to whether health effects are or are not being demonstrated. Professor Smith concluded that overuse and poor regulation of pesticides had profound effects on the distribution of chemicals in the environment and biosphere and that Silent Spring brought public and political attention to this and set in motion controlling and health regulations still with us today. However, pesticides (and other chemicals) are still required, and scientific risk assessment rather than risk perception should drive use and regulation of these substances.
In the next talk, Dr Joe Rodricks (Environ) gave a wider historical perspective with the title “In pursuit of safety: 100 years of toxicological risk assessment” (see pp 7-9 for Dr Rodricks’ article based on his presentation). Rodricks took us from Paracelsus, who identified that dose differentiates a poison from a non-poison, to Dr Alice Hamilton, who pioneered occupational epidemiology and industrial health in the early 20th century, and the 1906 Pure Food and Drug Act, which declared that food and drugs shall not contain adulterants that “may cause harm.” This Act led to the use of animal studies to characterise the effects of harm. Other pre-Silent Spring drivers of chemicals regulation included the recognition of occupational diseases (the American Conference of Industrial Hygienists, ACGIH, introduced exposure limits in the 1940s), the increase in post-war chemical production (leading to new safety requirements in the 1950s) and the identification of air and water pollution as a public health issue.
During the same period of time, cancers were also being studied and linked to chemical causes. By the 1950s there was a prevailing view that thresholds must exist for chemical toxicities, except for carcinogens, and Allowable Daily Intakes (ADIs) were being derived. These ADIs became targets even though no clear lines could be drawn between safe and unsafe and there is no way to quantify whether any reduction in exposures has led to adequate health protection. By the 1970s, a no threshold, linear dose model of cancer risk was adopted and, by and large, the system persists today. In 1983, the National Academy of Sciences issued the “Red Book” (Risk Assessment in the Federal Government: Managing the Process), which provided a standardised framework within which to undertake risk assessment. However, risk assessment per se does not enable decision-making. In 2008, the National Academy of Sciences published “Science and Decisions: Advancing Risk Assessment,” which calls for a unified and consistent approach to risk assessment. In the future, high throughput in vitro testing offers the potential for mode-of-action studies and better understanding of the inherent hazards of chemicals. In the continuing scientific and public debate about toxic hazards and their risks to health there is a need for greater, and improved, risk communication and public understanding of risk.
After lunch, the presentations moved from a historical perspective to the here-and-now. Dave Bench (HSE) started by giving an overview of UK pesticide regulations. Although pesticides have been used far back in history, their use did not become widespread until the 20th century. Before Silent Spring, pesticides were monitored through voluntary schemes such as the Crop Protection Products Approvals Scheme. These schemes developed over time but remained voluntary until the EC ruled that the UK was in breach of Community trading rules. This led to primary UK legislation, which has now been subsumed into the implementation of EU directives. The environmental risk assessment required for pesticide approval is rigorous, covering fate and behaviour in soil, water and air as well as toxicity studies on a number of non-target wildlife species and micro-organisms. Pesticides have developed over the last 50 years – they are generally no longer broad-spectrum and more targeted on specific pest biology. The number of active ingredients has also been reduced through the re-approval process to around 300 active ingredients. Bench stressed that the process was not static but that there were continuing developments in EU legislation, independent scientific scrutiny and new scientific evidence.
Following Carson’s work, DDT was banned in the US in 1972. Over the following decades, many countries across the globe followed suit, although some use continues today for indoor residual spraying to control malaria. However, even here there is ongoing controversy as to whether health effects are or are not being demonstrated. Professor Smith concluded that overuse and poor regulation of pesticides had profound effects on the distribution of chemicals in the environment and biosphere and that Silent Spring brought public and political attention to this and set in motion controlling and health regulations still with us today. However, pesticides (and other chemicals) are still required, and scientific risk assessment rather than risk perception should drive use and regulation of these substances.
In the next talk, Dr Joe Rodricks (Environ) gave a wider historical perspective with the title “In pursuit of safety: 100 years of toxicological risk assessment” (see pp 7-9 for Dr Rodricks’ article based on his presentation). Rodricks took us from Paracelsus, who identified that dose differentiates a poison from a non-poison, to Dr Alice Hamilton, who pioneered occupational epidemiology and industrial health in the early 20th century, and the 1906 Pure Food and Drug Act, which declared that food and drugs shall not contain adulterants that “may cause harm.” This Act led to the use of animal studies to characterise the effects of harm. Other pre-Silent Spring drivers of chemicals regulation included the recognition of occupational diseases (the American Conference of Industrial Hygienists, ACGIH, introduced exposure limits in the 1940s), the increase in post-war chemical production (leading to new safety requirements in the 1950s) and the identification of air and water pollution as a public health issue.
During the same period of time, cancers were also being studied and linked to chemical causes. By the 1950s there was a prevailing view that thresholds must exist for chemical toxicities, except for carcinogens, and Allowable Daily Intakes (ADIs) were being derived. These ADIs became targets even though no clear lines could be drawn between safe and unsafe and there is no way to quantify whether any reduction in exposures has led to adequate health protection. By the 1970s, a no threshold, linear dose model of cancer risk was adopted and, by and large, the system persists today. In 1983, the National Academy of Sciences issued the “Red Book” (Risk Assessment in the Federal Government: Managing the Process), which provided a standardised framework within which to undertake risk assessment. However, risk assessment per se does not enable decision-making. In 2008, the National Academy of Sciences published “Science and Decisions: Advancing Risk Assessment,” which calls for a unified and consistent approach to risk assessment. In the future, high throughput in vitro testing offers the potential for mode-of-action studies and better understanding of the inherent hazards of chemicals. In the continuing scientific and public debate about toxic hazards and their risks to health there is a need for greater, and improved, risk communication and public understanding of risk.
After lunch, the presentations moved from a historical perspective to the here-and-now. Dave Bench (HSE) started by giving an overview of UK pesticide regulations. Although pesticides have been used far back in history, their use did not become widespread until the 20th century. Before Silent Spring, pesticides were monitored through voluntary schemes such as the Crop Protection Products Approvals Scheme. These schemes developed over time but remained voluntary until the EC ruled that the UK was in breach of Community trading rules. This led to primary UK legislation, which has now been subsumed into the implementation of EU directives. The environmental risk assessment required for pesticide approval is rigorous, covering fate and behaviour in soil, water and air as well as toxicity studies on a number of non-target wildlife species and micro-organisms. Pesticides have developed over the last 50 years – they are generally no longer broad-spectrum and more targeted on specific pest biology. The number of active ingredients has also been reduced through the re-approval process to around 300 active ingredients. Bench stressed that the process was not static but that there were continuing developments in EU legislation, independent scientific scrutiny and new scientific evidence.
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Professor Alistair Boxall (University of York) then discussed the uptake and transformation of environmental contaminants. Carson was concerned that residues persisted in soil for many years and that they could become widely distributed and transferred to humans through bioaccumulation in animals. Boxall explained that analytical developments were partly responsible for increasing concern around contamination; we are able to detect ever-lower amounts of chemicals in the environment. Looking at octanol:water partition coefficients to predict bioconcentration factors, it can be seen that many pesticides mentioned in Silent Spring would now be classed as persistent and/or bioaccumulative (DDT has a degradation half-life of about 17 years). In contrast, very few of the current “UK top 50” pesticides would fall into these descriptions.
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Toa55/Shutterstock
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Professor Boxall then turned to the transformation of chemicals. Pesticides degrade into other compounds that may be more or less toxic than the parent compound. Historically these transformation products have not been monitored. Many transformation products can, for example, be detected in surface water, and they are often more persistent than the parent compound. The octanol:water partition coefficients are quite reliable for assessing neutral compounds, but the uptake of other compounds is much more reliant on the pH of the surrounding environment and individual organism characteristics. This is potentially important as half of all REACH pre-registered compounds are not neutral. Boxall finished with a statement from Carson on the uncertainties remaining and concluded that many of the points that she made remained valid.
Next, Steve Edgar (Vertase F.L.I. Ltd) presented a case study of contaminated land remediation at a former Bayer Crop Science site that was being redeveloped for housing. The site was heavily contaminated with agrochemicals, including pesticides and herbicides. During the public consultation, the work of Rachel Carson was raised and although there was an awareness of the issues there was little understanding. Nearby residents were concerned that remediation would churn up the contamination, rather than seeing the benefits of removing the contamination. A comprehensive site survey initially identified 217 chemicals of concern; this was prioritised down to 23. In total, about 1 million cubic metres of soil underwent processing, taking an average of 18 weeks treatment time. The risk communication issues with the public were the most challenging aspects of this work, and significant efforts went into communication and multi-agency co-ordination. The work was successfully completed with 96% contaminant removal from soil and more than 99% for water.
Following a refreshment break, Professor Stuart Harrad (University of Birmingham) looked at the changing profile of persistent organic chemicals. Whereas Carson was concerned with exposure to organochlorine pesticides, exposure profiles have since moved through polychlorinated biphenyls (PCBs) and dioxins and on to fluorinated and brominated compounds. Also, whereas historically environmental exposures have been mostly attributed to the diet, there is growing evidence that many of the new pollutants can be found in indoor dust as well, especially from flame retardants. For young children in the UK, exposure estimates indicate that intakes from dust would on average be similar to the dose from diet. However, 95th percentile dust exposures with a high dust intake would result in exposures three orders of magnitude greater than for diet. Studies correlating dust exposure and body burden are somewhat conflicting but both show a highly positive skewed distribution, with about 5-10% of samples/individuals more heavily contaminated. Some high-end exposure estimates for brominated diphenyl ethers (BDEs) show that guidance values might be exceeded, but the European Food Safety Authority (EFSA) recently concluded that current dietary exposure to hexabromocyclododecane in the EU does not raise a health concern and that additional exposure, particularly of young children, from house dust is also unlikely to raise a health concern. One of the challenges is the ongoing exposure due to extensive recycling and waste management of treated products. Furthermore, the chemical profiles are changing as new chemicals, such as chlorinated organophosphates, are introduced.
After a brief first-hand account of the still widespread use of DDT as a broad spectrum agricultural pesticide in Ethiopia, Dr Keith Tyrell (Pesticide Action Network UK) made a case for how the current pesticide regulations had failed to restrict the use of neonicotinoid pesticides. He referred to a number of studies demonstrating an association between the use of neonicotinoids and collapses of bee populations and outlined the situation in Italy, where bee populations appear to have recovered following a ban on the use of neonicotinoids. Dr. Tyrell discussed the limitations of the current regulations, which are primarily designed to assess spray applications of pesticides, whereas neonicotinoids are usually applied as a seed treatment resulting in a systemic pesticide. Tyrell also stressed that despite uncertainties regarding the environmental safety of neonicotinoids, there were currently no plans to restrict their use. In Tyrell's view this was counter to the precautionary principle where the onus is on the manufacturer to demonstrate unequivocal safety, not for the public to demonstrate harm.
Professor Ragnar Löfstedt (King's College London) concluded the meeting with a précis of his recent paper on Risk versus Hazard in Europe. He outlined fundamental differences between Member States, and even regulatory bodies within Member States, as to whether chemical regulation should be hazard- or risk-based. Certain areas of Europe (for example, Scandinavia) were predisposed to taking a hazard-based approach to chemicals whereas others, such as the UK, were much more in favour of risk assessment. However, Löfstedt also described how a Member State's approach could differ depending on the circumstances. For example, the Swedish government has stated a desire to phase out all hazardous chemicals by 2020 (hazard-based) but has vigorously defended the eating of pickled herring, shown to be contaminated with persistent chemicals (risk-based). These positions are political; Sweden has a very small chemical industry so, as a nation, would not be overly affected by tighter chemical regulation whereas the consumption of pickled herring is an issue of cultural heritage. Löfstedt outlined the need for greater risk communication and highlighted a number of efforts to bring about a better understanding of risk across Europe.
The meeting provided a diverse exploration of the areas where Rachel Carson's work has had an impact. Several speakers showed that Carson was not instrumental in developing these ideas (much work had started before Silent Spring), but she did “shine a light” on the issues and generated a momentum for change that has had a huge impact on chemical development, regulation and environmental assessment. Her work has, for example, led to the use of less persistent and less bioaccumulative pesticides. However, uncertainties remain, for example in the assessment of chemical mixtures. Perhaps the greatest challenge is how to better communicate risk and improve public understanding of risk.
Next, Steve Edgar (Vertase F.L.I. Ltd) presented a case study of contaminated land remediation at a former Bayer Crop Science site that was being redeveloped for housing. The site was heavily contaminated with agrochemicals, including pesticides and herbicides. During the public consultation, the work of Rachel Carson was raised and although there was an awareness of the issues there was little understanding. Nearby residents were concerned that remediation would churn up the contamination, rather than seeing the benefits of removing the contamination. A comprehensive site survey initially identified 217 chemicals of concern; this was prioritised down to 23. In total, about 1 million cubic metres of soil underwent processing, taking an average of 18 weeks treatment time. The risk communication issues with the public were the most challenging aspects of this work, and significant efforts went into communication and multi-agency co-ordination. The work was successfully completed with 96% contaminant removal from soil and more than 99% for water.
Following a refreshment break, Professor Stuart Harrad (University of Birmingham) looked at the changing profile of persistent organic chemicals. Whereas Carson was concerned with exposure to organochlorine pesticides, exposure profiles have since moved through polychlorinated biphenyls (PCBs) and dioxins and on to fluorinated and brominated compounds. Also, whereas historically environmental exposures have been mostly attributed to the diet, there is growing evidence that many of the new pollutants can be found in indoor dust as well, especially from flame retardants. For young children in the UK, exposure estimates indicate that intakes from dust would on average be similar to the dose from diet. However, 95th percentile dust exposures with a high dust intake would result in exposures three orders of magnitude greater than for diet. Studies correlating dust exposure and body burden are somewhat conflicting but both show a highly positive skewed distribution, with about 5-10% of samples/individuals more heavily contaminated. Some high-end exposure estimates for brominated diphenyl ethers (BDEs) show that guidance values might be exceeded, but the European Food Safety Authority (EFSA) recently concluded that current dietary exposure to hexabromocyclododecane in the EU does not raise a health concern and that additional exposure, particularly of young children, from house dust is also unlikely to raise a health concern. One of the challenges is the ongoing exposure due to extensive recycling and waste management of treated products. Furthermore, the chemical profiles are changing as new chemicals, such as chlorinated organophosphates, are introduced.
After a brief first-hand account of the still widespread use of DDT as a broad spectrum agricultural pesticide in Ethiopia, Dr Keith Tyrell (Pesticide Action Network UK) made a case for how the current pesticide regulations had failed to restrict the use of neonicotinoid pesticides. He referred to a number of studies demonstrating an association between the use of neonicotinoids and collapses of bee populations and outlined the situation in Italy, where bee populations appear to have recovered following a ban on the use of neonicotinoids. Dr. Tyrell discussed the limitations of the current regulations, which are primarily designed to assess spray applications of pesticides, whereas neonicotinoids are usually applied as a seed treatment resulting in a systemic pesticide. Tyrell also stressed that despite uncertainties regarding the environmental safety of neonicotinoids, there were currently no plans to restrict their use. In Tyrell's view this was counter to the precautionary principle where the onus is on the manufacturer to demonstrate unequivocal safety, not for the public to demonstrate harm.
Professor Ragnar Löfstedt (King's College London) concluded the meeting with a précis of his recent paper on Risk versus Hazard in Europe. He outlined fundamental differences between Member States, and even regulatory bodies within Member States, as to whether chemical regulation should be hazard- or risk-based. Certain areas of Europe (for example, Scandinavia) were predisposed to taking a hazard-based approach to chemicals whereas others, such as the UK, were much more in favour of risk assessment. However, Löfstedt also described how a Member State's approach could differ depending on the circumstances. For example, the Swedish government has stated a desire to phase out all hazardous chemicals by 2020 (hazard-based) but has vigorously defended the eating of pickled herring, shown to be contaminated with persistent chemicals (risk-based). These positions are political; Sweden has a very small chemical industry so, as a nation, would not be overly affected by tighter chemical regulation whereas the consumption of pickled herring is an issue of cultural heritage. Löfstedt outlined the need for greater risk communication and highlighted a number of efforts to bring about a better understanding of risk across Europe.
The meeting provided a diverse exploration of the areas where Rachel Carson's work has had an impact. Several speakers showed that Carson was not instrumental in developing these ideas (much work had started before Silent Spring), but she did “shine a light” on the issues and generated a momentum for change that has had a huge impact on chemical development, regulation and environmental assessment. Her work has, for example, led to the use of less persistent and less bioaccumulative pesticides. However, uncertainties remain, for example in the assessment of chemical mixtures. Perhaps the greatest challenge is how to better communicate risk and improve public understanding of risk.
