organisms. In organisms, trace elements are truly found at the level of traces. But
they can be present at much higher levels in the environment surrounding those
organisms. Lead is one of such trace elements. A widespread contamination by lead
over the Northern Hemisphere is the oldest large-scale known pollution caused by
human industry (Nriagu 1996). It dates back to the discovery of cupellation (a
metallurgical process for refining noble metals) 5,000 years ago, although it
increased largely 2,600 years ago with the introduction of coinage during the
Ancient Greek and Roman times. Smelting of metal ores in open fires caused the
emission of substantial amounts of lead and other metals to the atmosphere. After
the decline of the Roman Empire, a second pulse of lead pollution was caused by
the exploitation of silver mines in Central Europe during the Middle Age. A third
one occurred in modern times, starting with the Industrial Revolution during the
nineteenth century and peaking with the great expansion of motor vehicle traffic
since the end of the Second World War, in the period in which leaded gasoline was
used. Acute lead poisoning is known since the Ancient times, but it was not until
the 1960s and early 1970s that studies presented evidence that chronic exposure to
relatively low lead levels in the environment were causing neurological impairment
in subjects, especially children, with no clinical symptoms of toxicity (Needleman
2004). This finding was crucial to the banning of lead in gasoline (and also in paint
for domestic use) in the 1980s. Currently, there are international agreements to
further reduce emissions of lead and some other trace elements to the atmosphere
(UNECE 2016b).
The Pyrenees have not escaped pollution by trace elements. The sediments from
the lakes are a record of the history of pollution in the Pyrenees; changes in the
concentration of trace elements in layers of sediment deposited at different moments
reveal what was the contamination load at each time. Thus, for instance, the
analysis of sediments from Lake Redon (42°38′ N, 0°46′ E; 2240 m a.s.l.) in the
Central Pyrenees (Fig. 14.2) showed increasing levels of contaminating lead since
the 4th century BCE, a conspicuous peak during the ninth century CE, and a
modern peak starting in 1900 (Camarero et al. 1998). Furthermore, lead isotopic
composition changed in the peaks from the natural lead composition in the oldest
strata towards values closer to that of lead from mining activities. This pattern likely
results from the mixing of global, regional and even local influences. The onset of
the rise is in good agreement with the accepted global chronology of emissions. But
the tallest peaks are more reasonably attributed to mining in the surrounding areas,
although in the most recent one the influence of leaded gasoline cannot be distinguished from mining and probably also contributes.
Contamination of lake sediments by lead during the past centuries, if not longer,
is common in the Pyrenees. Almost with no exception, all lakes analysed show
increased values of lead with an isotopic composition that reveals its polluting
origin in the uppermost sediment layers (Bacardit et al. 2012). Other contaminating
trace metals such as cadmium, copper, mercury, nickel and zinc are often found
accompanying lead. Polluting trace elements are not equally distributed along the
whole Pyrenean range. An extensive lake survey showed that modern surface
sediments were enriched in lead and mercury with respect to deeper pre-industrial
330
L. Camarero
they can be present at much higher levels in the environment surrounding those
organisms. Lead is one of such trace elements. A widespread contamination by lead
over the Northern Hemisphere is the oldest large-scale known pollution caused by
human industry (Nriagu 1996). It dates back to the discovery of cupellation (a
metallurgical process for refining noble metals) 5,000 years ago, although it
increased largely 2,600 years ago with the introduction of coinage during the
Ancient Greek and Roman times. Smelting of metal ores in open fires caused the
emission of substantial amounts of lead and other metals to the atmosphere. After
the decline of the Roman Empire, a second pulse of lead pollution was caused by
the exploitation of silver mines in Central Europe during the Middle Age. A third
one occurred in modern times, starting with the Industrial Revolution during the
nineteenth century and peaking with the great expansion of motor vehicle traffic
since the end of the Second World War, in the period in which leaded gasoline was
used. Acute lead poisoning is known since the Ancient times, but it was not until
the 1960s and early 1970s that studies presented evidence that chronic exposure to
relatively low lead levels in the environment were causing neurological impairment
in subjects, especially children, with no clinical symptoms of toxicity (Needleman
2004). This finding was crucial to the banning of lead in gasoline (and also in paint
for domestic use) in the 1980s. Currently, there are international agreements to
further reduce emissions of lead and some other trace elements to the atmosphere
(UNECE 2016b).
The Pyrenees have not escaped pollution by trace elements. The sediments from
the lakes are a record of the history of pollution in the Pyrenees; changes in the
concentration of trace elements in layers of sediment deposited at different moments
reveal what was the contamination load at each time. Thus, for instance, the
analysis of sediments from Lake Redon (42°38′ N, 0°46′ E; 2240 m a.s.l.) in the
Central Pyrenees (Fig. 14.2) showed increasing levels of contaminating lead since
the 4th century BCE, a conspicuous peak during the ninth century CE, and a
modern peak starting in 1900 (Camarero et al. 1998). Furthermore, lead isotopic
composition changed in the peaks from the natural lead composition in the oldest
strata towards values closer to that of lead from mining activities. This pattern likely
results from the mixing of global, regional and even local influences. The onset of
the rise is in good agreement with the accepted global chronology of emissions. But
the tallest peaks are more reasonably attributed to mining in the surrounding areas,
although in the most recent one the influence of leaded gasoline cannot be distinguished from mining and probably also contributes.
Contamination of lake sediments by lead during the past centuries, if not longer,
is common in the Pyrenees. Almost with no exception, all lakes analysed show
increased values of lead with an isotopic composition that reveals its polluting
origin in the uppermost sediment layers (Bacardit et al. 2012). Other contaminating
trace metals such as cadmium, copper, mercury, nickel and zinc are often found
accompanying lead. Polluting trace elements are not equally distributed along the
whole Pyrenean range. An extensive lake survey showed that modern surface
sediments were enriched in lead and mercury with respect to deeper pre-industrial
330
L. Camarero