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Long-run exposure to low-dose radiation reduces cognitive performance

Science Direct, Journal of Environmental Economics and Management, Benjamin Elsner , Florian Wozny Volume 118, March 2023, 102785

Abstract

This paper examines the effect of long-run exposure to low-dose radiation on cognitive performance. We focus on the fallout from the Chernobyl accident, which increased the level of ground radiation in large parts of Europe. To identify a causal effect, we exploit unexpected rainfall patterns in a critical time window after the disaster as well as the trajectory of the radioactive plume, which determine local fallout but have no plausible direct effect on test scores. Based on geo-coded survey data from Germany, we show that people exposed to higher radiation perform significantly worse in standardized cognitive tests 25 years later. An increase in initial exposure by one standard deviation reduces cognitive test scores by around 5% of a standard deviation.

1. Introduction

The last 40 years have seen a drastic increase in radiation exposure. Today, the average person in Europe and America receives about twice the annual dose of radiation compared with in 1980 (NCRP, 2009). This increase is almost entirely due to man-made sources of radiation, such as medical procedures, nuclear power and nuclear weapons. Procedures such as CT scans, X-rays, mammograms or radiotherapy expose patients to low doses of radiation, and their use has been steadily increasing over the past decades. Moreover, the fallout from nuclear disasters such as Chernobyl and Fukushima or a nuclear bomb can expose people thousands of miles from the epicenter.

Medical research shows that subclinical radiation can damage human cells, which has potential knock-on effects on health and cognition and that these effects may occur at all ages. The existing literature has mostly focused on the effect of in-utero exposure, documenting significant adverse effects of radiation exposure during pregnancy on education and labor market outcomes many years later (Almond et al., 2009, Heiervang et al., 2010, Black et al., 2019). However, there is little evidence on the long-term effects of exposure to low-dose radiation after birth. Documenting such effects is important, not least because of the number of potentially affected people: the number of people alive at any one point is substantially greater than the number of fetuses in the womb.

In this paper, we exploit plausibly exogenous variation of the Chernobyl fallout to study the impact of exposure to low-dose radiation on cognitive test scores 25 years after the disaster. We focus on Germany, which received a significant amount of fallout due to weather conditions in the aftermath of the disaster in 1986. Because of the long half-life of the radioactive matter, people who continuously lived in areas with higher initial fallout have been exposed to higher radiation levels for over 30 years. For people exposed after birth, there are two plausible biological channels through which radiation can affect cognitive test scores: a direct effect on the brain because radiation can damage brain cells, and an indirect effect through general health, which may lead to fatigue, thus reducing test performance.

Our dataset – the National Educational Panel Study (NEPS), a representative geo-coded survey – allows us to link fine-grained data on fallout levels in a person’s municipality of residence since 1986 to a battery of standardized cognitive tests done 25 years after the disaster. At the time of the disaster, over half of our sample were adolescents or adults, allowing us to estimate the long-run effect of exposure at these ages.

The central identification challenge is a potential correlation between the local amount of radiation and residential sorting. The local amount of radiation is driven by a combination of several factors, for example wind speed, rainfall, altitude or soil composition. Some of these factors may have also influenced residential sorting prior to 1986, thus potentially leading to omitted variable bias. ………………………………………………………………………

Our central finding is that people exposed to higher levels of radiation from 1986 onward performed significantly worse in cognitive tests 25 years later. A one-standard-deviation higher initial exposure in 1986 reduces test scores by around 5% of standard deviation. Over the course of 25 years, the additional radiation dose of a one-standard-deviation higher initial exposure is roughly equivalent to the dose from 6 chest X-rays or 1.65 mammograms, which indicates that the long-term effects of low-dose radiation can be non-trivial. An additional analysis shows that these effects are not driven by selective migration after the Chernobyl disaster.

This result feeds into two domains of the public debate on radiation. One is about the costs and benefits of nuclear power in many countries. While nuclear power offers the advantage of supplying vast amounts of energy at zero carbon emissions, it comes with the cost of potential disasters. In the last 35 years we have seen two major disasters. Given the proliferation of nuclear power along with the emergence of conflicts like the current war in Ukraine, it is possible that more nuclear disasters may follow. Our results, along with those in other studies, point to significant external costs of nuclear power generation and document an important effect of nuclear disasters on the population. Another public debate, more broadly, deals with exposure to man-made radiation. For example, today the average American receives twice the annual radiation dose compared to in 1980, which is mainly due to medical procedures such as X-rays, mammograms or CT scans (NCRP, 2009). Our results can inform the debate about the long-term consequences of this increase in radiation exposure. The radiation dose from medical procedures is similar to the additional radiation dose Germans in highly affected areas received after Chernobyl. And although these procedures offer high benefits for patients, our findings suggest that they come with a health cost due to a higher radiation exposure.

With this paper, we contribute to three strands of literature. First, our findings contribute to the literature on the effect of pollution on human capital. This literature has produced compelling results for two types of effects. One strand focuses on exposure during pregnancy or early childhood and documents adverse long-term effects of pollution. Another strand focuses on adults and estimates the short-run effect of fluctuations in pollution on outcomes such as productivity, test scores and well-being.¹ Our study, in contrast, examines the long-run effects among people exposed after early childhood. These effects are important, not least because of the number of people affected. The cohorts in our sample represent around 24 million people, compared to 200,000 children who were in the womb at the time of Chernobyl. Even if the individual effect is smaller for people exposed after early childhood, our study shows that the environment can have adverse consequences for large parts of the population and, therefore, exposure after early childhood deserves more attention in the literature.

Second, this paper adds new evidence to the emerging literature on pollution and cognitive functioning……………………………………………………….

……………………., this paper contributes to the broader literature on the effects of low-dose radiation. Two recent reviews of the epidemiological literature by Pasqual et al. (2020) and Collett et al. (2020) conclude that there is significant evidence that exposure to low-dose radiation early in life has negative effects on health and cognitive performance.

……………………………….. our results point to even wider-reaching adverse effects of nuclear disasters. Germany is over 1200 km from Chernobyl, and our study shows that large parts of the population have been adversely affected.

2. Historical background and review of the medical literature

2.1. The Chernobyl disaster and its impact in Germany

2.1. The Chernobyl disaster and its impact in Germany

The Chernobyl nuclear disaster in 1986 is one of the two largest nuclear accidents in history. It occurred after a failed simulation of a power cut at a nuclear power plant in Chernobyl/Ukraine on April 26, 1986, which triggered an uncontrolled chain reaction and led to the explosion of the reactor. In the two weeks following the accident, several trillion Becquerel of radioactive matter were emitted from the reactor, stirred up into the atmosphere, and – through strong east winds – carried all over Europe.² The most affected countries were Belarus, Ukraine as well as the European part of Russia, although other regions, such as Scandinavia, the Balkans, Austria and Germany also received considerable amounts of fallout. The only other accident with comparable levels of fallout was the Fukushima disaster in Japan in 2011 (Yasunari et al., 2011).

Post-Chernobyl radiation in Germany.

………………………………….From 1986 to 1989, the governments of West and East Germany rolled out a comprehensive program to measure radiation across the country. At over 3,000 temporary measuring points, gamma spectrometers measured the radiation of Cs137. Based on the decay of the isotopes, all measurements were backdated to May 1986.

………………………………………….Radiation exposure of the German population.

Humans can be exposed to radiation in three ways, namely through inhaling radioactive particles, ingesting contaminated foods, as well as external exposure, whereby radiation affects the body if a person is present in a place with a given level of radioactivity in the environment. Exposure to radiation through air and ground can be directly assigned to – and therefore be strongly correlated with – a person’s place of residence ……………………………………………………………………………………………………………………………..

Information about the nuclear disaster and reactions of the German public

……………………………………………………………………………………. 2.2. Effects of radiation on the human body

The effect of radiation on the human body is by no means limited to high-dose radiation, such as the one experienced by survivors of nuclear bombs or clean-up workers at the site of the Chernobyl reactor. The medical literature has shown that exposure to subclinical radiation – at doses most people are exposed to, for example due to background radiation, medical procedures, or the fallout from Chernobyl in large parts of Europe – can negatively affect cognition, physical health and well-being. Moreover, while the effects of subclinical radiation may be strongest during pregnancy and early childhood, radiation exposure can have adverse effects throughout a person’s life.

Plausible channels.

Radiation exposure can affect cognitive test scores through four types of channels:

• 1.A direct effect on cognition, as radiation can impair the functioning of brain cells.
• 2.An indirect effect through physical health; radiation can impair the functioning of organs and lead to greater fatigue, which in turn may negatively affect test scores.
• 3.An indirect effect through mental health; a review by Bromet et al. (2011) suggests that people’s worry about the long-term consequences of radiation for physical health may lower their well-being and lead to poor mental health.
• 4.Indirect effects through behavioral responses, such as internal migration or changes in life style. To the extent that these effects reflect avoidance behavior, they will dampen the negative biological effects.⁵

In the following, we summarize the evidence from two types of study: one based on observational studies with humans, the other based on experimental studies with mice and rats. While both arguably have their weaknesses – one is non-experimental, the other has limited external validity – together they show that an effect of radiation on cognitive test scores is biologically plausible.

Observational studies.

The effect of radiation on cognitive performance is an active field of research in radiobiology and medicine.  Radiation affects the human body through ionization, a process that damages the DNA and can lead to the dysfunction or death of cells (Brenner et al., 2003). Until the 1970s the human brain was considered radio-resistant, that is, brain cells were assumed to be unaffected by radiation. This view changed when lasting cognitive impairments were found in cancer patients who underwent radiotherapy. Studies find cognitive impairments among 50%–90% of adult brain cancer patients who survive more than six months after radiotherapy. The cognitive impairment can manifest itself in decreased verbal and spatial memory, lower problem-solving ability and decreased attention, and is often accompanied by fatigue and changes in mood ……………………………………………….

Laboratory evidence on rats and mice.

The experimental evidence with rodents confirms the evidence found among human cancer patients. Rats who were treated with brain irradiation experience a reduction in cognitive ability, although the biological processes differ between young and old rats………………………………………

While these studies confirm that radiation can plausibly affect cognitive functioning across the life cycle, they are mostly based on once-off radiation treatments. In contrast, after Chernobyl, the German population was constantly exposed to higher ground radiation for many years. A recent experiment on mice by Kempf et al. (2016) is informative about the effect of regular exposure to low-dose radiation. Among mice who were exposed for 300 days, the researchers detected a decrease in cognitive functioning and a higher incidence of Alzheimer’s disease.

Impact on overall health……………………………………….

3. Data and descriptive statistics…………………………………………………..

3.1. The NEPS data

Our main data source is the NEPS, a rich representative dataset on educational trajectories in Germany. ………………………………………………………………………………………………….

3.2. Estimation sample

Our sample includes all survey participants who were born before Chernobyl. We exclude participants born after Chernobyl because the survey only sampled birth cohorts up to December 1986, leaving us with few participants who were born after Chernobyl. Moreover, because we are interested in the effect of post-natal exposure, excluding them ensures that our estimates are not confounded by exposure in utero, which operates through a different biological channel. ……………………………………………………………………………………………………………………………………..

3.3. Cognitive tests………………………………………………………………………………………………………

3.4. Municipality- and County-level Data

Data on ground deposition……………………………………………………………………………………………

Linkage between individual and regional data.………………………………………………………………………..

Additional data.…………..

3.5. Descriptive statistics………………………………………………………………………………………………………………………………………..

4. Empirical strategy

4.1. Empirical model………………………………………………………………………………………

4.2. Identification challenge and balancing checks……………………………………………………………………………………

4.3. Instrumental variable strategy……………………………

IV component I: local rainfall during a critical time window.………………………………………………………………………………….

IV component II: available radioactive matter in the plume……………………………………………………………

First stage and instrument relevance………………………………………………………………………………..

Instrument validity………………………………………………………………………………………………………………

5. Radiation and cognitive skills: Results

5.1. The effect of initial exposure on cognitive performance………………………………………………………………….

5.2. The effect of average exposure,1986–2010…………………………………………………

5.3. Internal migration as a potential channel………………………………………………………………

5.4. Effect magnitude and discussion…………………………………………………………………

5.5. Robustness checks………………………………………………………………………..

6. Conclusion

In this paper, we have shown that radiation – even at subclinical doses – has negative long-term effects on cognitive performance………………………………………………………………………………………..

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Appendix A. Supplementary data………………………………….. more https://www.sciencedirect.com/science/article/pii/S0095069623000037

August 17, 2024 - Posted by Christina Macpherson | Germany, radiation, Reference