9
NARRATIVE
Lead toxicology
Lead is a highly toxic poison that affects most body systems,
resulting in death at high exposures, and a range of adverse
physiological and behavioural impacts at lower exposures.
There is no safe threshold of exposure. Unlike many other trace
metals it has no physiological function. It acts as a neurotoxin,
affecting multiple aspects of animal (and thus human)
behaviour and causing brain damage at low levels of exposure
in the absence of other symptoms. Developing individuals
(children) are particularly at risk (Flora et al. 2012).
Its physical properties i.e. density, malleability, low melting
point, tensile strength and resistance to corrosion in particular
– together with availability and relative cheapness, has meant
that the metal has long been of value to human society.
Indeed, our word‘plumbing’derives from the lead’s Latin name
plumbus owing to its use in Roman water supply systems.
Lead in antiquity
The history of environmental pollution by lead is as long
as its history of use by human society (Settle and Patterson
1980, Hong et al. 1994, Hernberg 2000). Both the Egyptians
and Hebrews used lead and the Phoenicians mined the ore
in Spain c. 2,000 BCE. Hernberg (2000) notes the earliest
written account (on an Egyptian papyrus scroll) as a record
of homicidal use of lead compounds. Two thousand years
ago, lead was in wide and regular use by the Greeks and
Romans given its ready accessibility as a by-product of silver
production, and the practical consequences of its physical
properties. Significant lead production commenced c. 5,000
years ago with the discovery of smelting techniques for lead
sulphide ores (galena). Its geological co-occurrence with silver
(of significance for coinage) resulted in an increasing extent
of lead production over the next 2,000 years, with mining
and smelting in Spain representing c. 40% of worldwide lead
production during Roman times (Hong et al. 1994). Roman
production has been estimated at 60,000 tonnes per annum
for 400 years (Hernberg 2000). The environmental emission of
air-borne lead particles from these early Roman mining and
smelting activities have given a record of changing deposits
not only within the Greenland ice-cap (the first evidence of
anthropogenic hemispheric-scale lead pollution (Hong et al.
1994)), but also in wetlands across the whole of Europe (Shotyk
et al. 1998, Renberg 2001). The source has been isotopically
distinguished from naturally occurring emissions sources such
as sea spray and volcanic eruptions.
Archaeological evidence exists to demonstrate both the
significant contamination of local environments with lead (e.g.
Delile et al. 2014), and the toxicity resulting from production
and some aspects of use (Waldron 1973, Retief and Cilliers 2005
and references therein). Indeed, the risk of acute poisoning
had been recognised by Pliny the Elder in the first century CE:
“While it is being melted, all the apertures in the vessel should
be closed, otherwise a noxious vapour is discharged from the
furnace, of a deadly nature, to dogs in particular.” Pliny noted
that lead poisoning was common among shipbuilders, whilst
Dioscerides – a physician in Nero’s army in the same period –
observed that “Lead makes the mind give way.”
The main uses of lead at this time were for plumbing; for
domestic utensils made from lead and pewter (an alloy of lead
and tin) or use of pottery with lead glazes; and as a sweetener
used in the production and storage of wine. Lead plates were
dipped in wine during fermentation to counter-act the acidity
of grape juice, and lead acetate (“sugar of lead”) added to
sweeten the taste. Use of lead-lined storage vats also resulted
in significant concentrations within wine (Waldron 1973,
Needleman and Gee 2013).
There is no doubt that there was significant exposure to lead
frommultiple sources in Roman society. However, the extent to
which chronic exposure to lead was significant in the collapse
of the Roman civilisation remains academically contested and
has been reviewed by Gilfillan (1965), Nriagu (1983) and Retief
and Cilliers (2005) among others.
Global lead production fell with exhaustion of Roman lead
mines around 2,000 years ago leading to parallel declines in
lead concentrations in Greenland ice and European wetlands,
presumably related to reduced smelting activity (Settle
and Patterson 1980, Hong et al. 1994, Shotyk et al. 1998,
Renberg 2001).
Regulation of some sources of lead poisoning