First published in 1962, Rachel Carson’s book “Silent Spring” is considered the most influential book in the fields of Toxicology and chemical pollution. Carson drew public attention to the massive spraying of organochlorine pesticides that were occurring in the USA and throughout the world at the time, and the detrimental effect these pesticides were having on the environment, humans and wildlife, particularly on birds.
However, despite the best efforts of regulators, scientists, and the Environmental Movement as a whole, there are still detrimental effects from the release of substances into the environment on both ecological and human health. Some of these are mausoleums of past malpractice, in the form of breakdown resistant organochlorines and other POPs (persistent organic pollutants,) to new consequences such as EDCs (endocrine disrupting chemicals) and large-scale toxic metal production from the computer industry.
In this essay, I will attempt, to sum up the last fifty-four years of Environmental Science, and answer the question, have the harmful effects of chemicals upon man and wildlife decreased since Silent Spring.”
I will try and take a worldwide perspective discussing developed and developing countries wherever possible and include the main pollution groups, Organics and especially POPs, Gaseous pollutants, Inorganics and organometallics, Radioactive pollutants,
Organic Pollutants
Organic compounds are a vast and diverse group of chemicals (there are, as of the time of writing 66,777,604 chemicals on the CAS registration database1, 2), so it’s no surprise that organic pollutants are the most diverse group. In this section, I shall focus on Persistent Organic Pollutants.
Persistence organic pollutants have a number of chemical properties that make them highly damaging pollutants. They are lipophilic, hydrophobic, resistant to biological breakdown. There lipophilic and resistance to biological breakdown means that they easily bio-magnify up food chains, and have syncs in soils, and can be easily transported by particulates in air and water3. Many of them also are able to mimic hormones, acting as Endocrine disrupting chemicals (EDCs)
Table 1- Indication of group transport routes, group exposures sources, group production group sources and group Harmful effects of the types of POPs
POP Name
|
Transportation and exposure
|
Sources
|
Example Harmful Effects
|
Polychlorinated Biphenyls
|
|
|
|
Polychlorinated dibenzodioxins & dibenzofurans (PCDDs & PCDFs)
|
|
|
|
Polycyclic aromatic hydrocarbons (PAHs)
|
|
|
|
Organochlorine (OC) Pesticides
|
|
|
|
Polychlorinated biphenyls
Human exposure around the world and historically
PCBs are found in measurable levels in every environment, in every animal and probably every human on earth. 2Manufacturing started in the 1920s, accelerated after the second world war and reached a peak during the 1960s and early 1970s. Manufacturing had halted by the 1980s in most countries (notable exception, North Korea, production under review in 2012) around the world. In total around 1-1.5 million tonnes of commercial PCBs are known to have been produced. There has been no known production on the African continent, although PCBs were imported. 2
However, despite these successes, PCBs remain a concern for human heath, background levels in humans, although have gone down substantially since the 1970s are still of concern. 2
In Europe, 5 monitoring programs to do with PCBs and breast milk have been conducted. In 2009-2012 the levels ranged from 12-79 ng/g lipid9. In 1987-1988 levels ranged between 150 to 734 ng/g9. The median for the US has decreased from 206 to 63.6 between 1987-20039. In Japan, a study from Osaka showed decreases from 1.1302 ug/g in 1972 to 0.0076 ug/g in 199810.
Wildlife exposure
PCBs were first detected in wild bird tissues and eggs in 1965 and were identified by Jensen in 196611. In 1969 large amounts of pelagic birds died off the coast of the UK and were found to have PCBs levels of several hundred ppm, a larger amount than had been detected before12. Levels were measured in Grebes in the UK in 1967 by Presst et al and were found to be as to average 35.8 ppm. Much higher level where found in fish predatory birds where levels as high as 900ppm where seen12, Similar levels were found in Sweden (Jensen et al 1969.)These levels are much higher than those seen today in European, for example, Murvoll et al found the level of total PCBs were 16.128 ppm in the Norwegian Shag13. A long-term monitoring survey performed in Sweden found that total PCBs decreased by an average of 3 percent per year between 1967-1995. The UN Monitoring program WEOG monitoring program found a steady decline in total PCBs in the air since the 1990s, although it has slowed since 2000 and some of the lighter cogenitors have recently increased. 9
In Latin America and the Caribbean (GRULAC region for the Stockholm Convention) long-term monitoring data could not be found and there is insufficient monitoring to determine a trend for the whole region. The mean background rural air concentrations was 61.73 pg/M3 (range 0.06 to 399.00 pg/M14.
In Asia, numerous monitoring programs exist. Japan has had a monitoring program since the 1970s. This has shown air levels decreased from over 100 ng/M3 in the early 1970s to <1 2005.10="" br="" in="" ng="">
Metals and organometallics
Metals are another group of highly problematic pollutants. Some metals are necessary for homoeostasis, such as Calcium, Iron, Zinc, Copper, Magnesium, so some exposure is beneficial, although high doses are toxic15. Others such as Mercury, Lead, Silver, Cadmium have no known biological function are therefore always pollutants15. Metals are naturally occurring and therefore naturally present in small amount in the environment through chemical breakdown of naturally occurring ores. However, anthropogenic sources such as mining, refining, combustion often release far more heavy metals in the environment (this can be shown through the use of Anthropogenic Enrichment Factors.) Metals can contaminate land for hundreds of years after the releases as they bind strongly to clay soils and are not biodegradable.16
Some inorganic metals can also be bound to organic ligands, becoming an organometallic. These can be formed naturally by the action of certain bacteria or be manufactured for human use (e.g. Tributyltin.)16 Organometallics often have different effects and environmental fates than their inorganic counterparts. They also adversely affect water supplies because they can be transported at higher pH levels, thus more easily seeping into drinking water. 16
The effects and exposure routes of the most concerning metal pollutants are given below.
Name
|
Exposure Routes (human)
|
Exposure Symptoms
|
Lead
|
Lead Paint, Lead piping, Inhalation (combustion of leaded petrol), occupational exposure, food and drink, Tobacco17
|
GI disorders, stomatitis, tremor, haemoglobinuria, ataxia, paralysis, vomiting, convulsion, depression, impaired neurological development, kidneys cardiovascular joint, reproductive systems disorders, psychosis.
|
Mercury
|
Food and drink (Minamata Bay,) occupational exposure, inhalation (released from combustion of coal and waste)18
|
GI disorders, stomatitis, tremor, haemoglobinuria, ataxia, paralysis, vomiting, convulsion, depression, Spontaneous abortion, congenital malformation
|
Arsenic
|
Food and Drink, Inhalation, Occupational Exposure19
|
GI disorders, stomatitis, tremor, haemoglobinuria, ataxia, paralysis, vomiting, convulsion, depression20
|
Cadmium
|
Tobacco, Food and drink, inhalation, Occupational18
|
renal dysfunction, obstructive lung disease, bone defects, increased blood pressure and myocardial dysfunctions, pulmonary oedema, death21
|
Tributyltin
|
Anti-Fouling Paints, Marine Food, Preserved Wood22
|
Endocrine disruption, developmental effects, imposex 23
|
Lead
Human Exposure to Lead
The blood exposure of lead has been declining overall around the world. In the USA the general mean in adults decreased from 13.1 to 1.8 ug/dL between 1976-2000 according to Pickle et al (1994) and the CDC (2003a) (it's worth noting that these studies included smokers so decrease in non-smoking adults will be more.) In Australia, decreases have also been found. 17In developing world old data is sparse, making an assessment of long-term changes difficult, however Lead was only below the recommended level of 10ug/dL of blood in all but 2 rural areas of South Africa. In Asia, most values were <10 13.3="" 17="" 1985-1998.="" 1990s="" a="" adults="" between="" br="" decreases="" dl.="" dl="" due="" early="" eastern="" effect.="" europe="" expected="" exposed="" fall="" for="" found="" have="" high="" higher="" however="" in="" is="" japan="" lead="" leaded="" levels="" non-occupationally="" of="" one="" only="" petrol="" phase-out="" significant="" soviet="" study="" substantial="" than="" the="" to="" ug="" union.="" urinary="" was="" were="">
For children, decreases of between 25% to 45% have been seen in the Belgium, Canada, Germany, New Zealand, Sweden and the United Kingdom. Dramatic, if uneven (lead still adversely affects poor, non-white families in urban areas and older housing, with 1.5% of children showing Lead levels of >15ugdL) decreases have seen also in the USA. Several Countries in Asia have a level between 5-15 ug/dL with levels higher than 10ug/dL associated with Lead industry. 17
Although no clear global trend can be determined for decreasing lead levels can be determined from available data, it is clear that lead remains a significant problem in developing countries in Africa and eastern Europe. In developed countries, however, concerted efforts reduce the amounts of Lead in the environment have had effects. The worldwide phase-out of leaded petrol in all countries apart from Algeria, Yemen, Iraq, Myanmar, Afghanistan, North Korea, will hopefully have a large effect of lead exposure from inhalation in urban areas 17
Tributyltin
Tributyltin was first created in the 1920s and saw wide use as an anti-fouling paint on ships, in industrial applications as a slime control and as a wood preserver. It was widely excepted to be broken down to inorganic tin in the environment, however, it's half-life in sediment is in the tens of decades range. It is the most significant pesticide in fresh and marine waters in Europe. 22Marine Wildlife Exposure.
The levels in marine life have been decreasing over the past 30 years, with levels as higher than 500 ng/l recorded before widespread bans took place in the 1980s24, with marine waters now rarely exceeding 100 ng/l.25 Sediment levels have also decreased, however, temporal trends for specific countries as difficult to show due to inconsistent sampling and hotspots associated with high levels of shipping, with levels as high as 14,000 ng/l in Japan26.
Dramatic decreases have also been seen in fish, marine plants and in Europe, Oceania and Japan. Three studies have shown decreases in TBT levels in fish from Europe, the Oceania countries and Japan since it was banned in these locals27 28 29. However, TBT contamination still remains widespread and has been shown to be very hazardous in counties with no or weakly enforced (samples from Bahrain showed sea water levels as high as 17.9 ug/l30.)
It also established a body to review and assess progress and to recommend additional compound be added to the convention. 31
Also worth mentioning are the water framework directive for integrating a whole catchment approach to water management, Regulation[EC]No1107/2009 for introducing a no go clause for Persistent organic pollutants, carcinogenic, mutagenic or reprotoxic, persistence bioaccumulative, toxic or very persistent- very bioaccumulative to the regulation of plant protective products (these rules are not true of other chemicals, however, they have to be registered under the REACH agreement.)31
Human Exposure
Despite public concern over exposure to TBT, there has been little publish studies on human dietary load. There have been a few studies of marine life borough at markets and then extrapolated to estimate exposure through food using national average fish intakes. Studies in Asia, North America and Europe all show that inputs from eating fish are unlikely to contribute more than allowed dietary intake of 0.25ug/ kg / d. A study in Finland found that at-risk individuals (children) who consume high levels of fish may be at risk from TBT effects, although the levels were still below the 0.25ug figure. The only dietary levels higher than 0.25 ug/ kg/ l were found in fishermen from the Hsiangshan coastal area of Taiwan. 22Regulation of Pollutants
A number of effective environmental regulations have come into force in the past 30 years. I shall briefly mention a few here.Stockholm Convention of POPs 2004
The fist worth mentioning is the Stockholm Convention on Persistence Organic Pollutants. This international agreement sets out to actions for the ‘dirty dozen’ as outlined below
Chemicals or Chemical group
|
Action
|
Aldrin, chlordane, dieldrin, endrin, heptachlor, hexachlorobenzene (HCB), mirex and toxaphene, PCBs,
|
Elimination of all use
|
DDT
|
Use for disease control until affordable and effective alternative
|
Dioxins and Furans (including PCDDs, PCDFs)
|
Minimization and where possible elimination of accidental production
|
It also established a body to review and assess progress and to recommend additional compound be added to the convention. 31
Various National Laws against Tetraethyl Lead (TEL) in road Vehicles
As of 2015, the vast majority of countries have a complete ban on the use of TEL in motor fuels. Because TEL was responsible for 80-90% of airborne lead in urban areas worldwide, this has reduced lead levels in those areas significantly. For example, reduction of >70% was seen in US, Ontario and the UK as TEL was reduced. 31Also worth mentioning are the water framework directive for integrating a whole catchment approach to water management, Regulation[EC]No1107/2009 for introducing a no go clause for Persistent organic pollutants, carcinogenic, mutagenic or reprotoxic, persistence bioaccumulative, toxic or very persistent- very bioaccumulative to the regulation of plant protective products (these rules are not true of other chemicals, however, they have to be registered under the REACH agreement.)31
Summary
Although there is plenty of evidence of wide-ranging effects from diverse types of pollutants in the global environment today, effective legislation such as the Stockholm Convention of POPs and the numerous national regulations on TBT have reduced the sources and presence of environmental pollutants, and thus the effects of envioromental pollutants significantly.
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