Rome’s urban history inferred from Pb-contaminated waters trapped in its ancient harbor basins

Abstract

Heavy metals from urban runoff preserved in sedimentary deposits record long-term economic and industrial development via the expansion and contraction of a city's infrastructure. Lead concentrations and isotopic compositions measured in the sediments of the harbor of Ostia-Rome's first harbor-show that lead pipes used in the water supply networks of Rome and Ostia were the only source of radiogenic Pb, which, in geologically young central Italy, is the hallmark of urban pollution. High-resolution geochemical, isotopic, and C analyses of a sedimentary core from Ostia harbor have allowed us to date the commissioning of Rome's lead pipe water distribution system to around the second century BC, considerably later than Rome's first aqueduct built in the late fourth century BC. Even more significantly, the isotopic record of Pb pollution proves to be an unparalleled proxy for tracking the urban development of ancient Rome over more than a millennium, providing a semiquantitative record of the water system's initial expansion, its later neglect, probably during the civil wars of the first century BC, and its peaking in extent during the relative stability of the early high Imperial period. This core record fills the gap in the system's history before the appearance of more detailed literary and inscriptional evidence from the late first century BC onward. It also preserves evidence of the changes in the dynamics of the Tiber River that accompanied the construction of Rome's artificial port,, during the first and second centuries AD.

Economic resilience of Carthage during the Punic Wars: Insights from sediments of the Medjerda delta around Utica (Tunisia)

“…First, the residual fraction left over after leaching a sample in the laboratory corresponds to the Pb contained initially in the mineral crystal lattice during rock formation and hence is referred to as natural, crustal, or detrital since it characterizes the local geogenic Pb background (26). Secondly, the leachate fraction (or extractable phase) represents the labile or anthropogenic component of the sample Pb, which is adsorbed onto sediments once released from an independent anthropogenic source (11,26). This anthropogenic component (e.g., lead pipes, gasoline, coal, aerosols, etc.)…”

“…This natural Pb isotopic composition is also easily readable using the geochemically informed parameters T mod [Pb model ages in million years (Ma)] and κ (the 232 Th/ 238 U ratio), which are derived from the time-integrated Pb isotopic compositions using the equations given by Albarède et al (27). The advantages of this representation over that based on raw Pb isotopic ratios have been demonstrated in a number of geological (28), archaeological (27), and geoarchaeological contexts (11 i) The 69 Pb-polluted sediments differ from the unpolluted samples in both their Pb content and Pb isotopic composition. Lead concentrations and EF Pb range between 10 and 210 ppm (mean = 59.1 ppm) and 2.13 and 20.9 (mean = 6.9), respectively ( Fig.…”

“…Our knowledge of ancient mining centers (i) is focused mainly on Roman mining districts (a question of textual sources?) (6,7), (ii) tends to emphasize major centers to the detriment of smaller ones (8), and (iii) concerns Central and Western Europe more than North Africa (5)(6)(7)(9)(10)(11)(12), often without robust chronological timelines (7). This paradox is all the more striking when one observes the spatial distribution of lead-silver mines within the Roman Empire, which is largely devoid of them along its southern and eastern fringes (5)(6)(7).…”

“…At much smaller local scales, such as the area of a city, the Pb paleopollution approach is less ambiguous about the source since the distances traveled by anthropogenic lead pollution are short and the routes well established; they follow the urban hydrographic network. Studies of Pb paleopollution trapped in fluviomarine sediments of ancient harbor basins have thus been able to document unexpected and intriguing facets of urban history in a number of ancient cities around the Mediterranean (10,11,21). These metal paleopollutions trapped in harbor sediments could not have come from aerosols as these contain very low levels of lead, even during episodes of intense atmospheric pollution.…”

“…These metal paleopollutions trapped in harbor sediments could not have come from aerosols as these contain very low levels of lead, even during episodes of intense atmospheric pollution. For example, during the Roman period, when lead contamination of the atmosphere was widespread, the proportion of pollutant lead did not exceed ∼10 ppm in European lake deposits (20) and a few ppt in Greenland ice (5), while, at the same time, port sediments were several hundred ppm above the natural Pb abundance level (11). The difference-an order of magnitude or more-is far too large to consider aerosols as a credible source of lead contamination of fluviomarine sediments.…”