Lead is a chemical chameleon. It resembles calcium so closely that the body takes it up as if it were a nutrient, and precisely where calcium is needed, in the nervous system and in the bones, it does its damage. At ETH Zürich we used lead isotopes as geological clocks: the ratio of the lead isotopes reveals the age of a rock. The same analysis answers a different question in a building, namely whether lead is present in paints, pipes and dust.
Where lead occurs in buildings
Three sources are typical, especially in buildings up to the 1970s:
- Lead paints: lead white (lead carbonate) in light-coloured paints, red lead (orange) as rust protection on metal, lead chromate in yellow and green tones. In Gründerzeit and Art Nouveau buildings they often lie beneath several newer layers. Intact, they are unproblematic; the risk arises when they flake or when work raises dust.
- Lead pipes: lead water pipes are found above all in the oldest building stock. The City of Vienna locates the main problem in the lead installations of Gründerzeit buildings, constructed up to 1938; the lead house-connection pipes there were replaced by 2007, yet in many old buildings the pipes inside the apartment were left in place, so that the last stretch to the tap can still be lead.
- Lead dust: the underestimated source. Weathering lead paint produces fine dust that accumulates on window sills, floors and in cracks, especially relevant in households with small children.
A brief look at the history
Lead pigments are ancient. Lead white, chemically basic lead carbonate, was the most important white pigment of all until the end of the 19th century (ColourLex); red lead, the orange-red lead oxide, served as a rust-protective primer directly on iron and steel, and lead chromate, as chrome yellow, supplied strong yellow tones (IARC 2006). Their toxicity was recognised early: as far back as 1921 the International Labour Organization adopted Convention No. 13, the so-called Geneva White Lead Convention, which obliged ratifying states to prohibit lead white and lead sulphate in the interior painting of buildings (with narrow exceptions). Austria ratified on 12 June 1924.
Over the course of the 20th century, lead white disappeared from paintwork: bans and restrictions on lead white in interior painting clustered between 1905 and 1930 in most countries, according to the literature relayed by van Driel et al. (2018), and lead white was replaced by less toxic white pigments such as zinc white and titanium white (ColourLex). At European level, lead carbonates and lead sulphates were later restricted as a paint constituent, today under the REACH Regulation, with an exception now only for the restoration of works of art and historic buildings, which refers explicitly to that ILO convention of 1921. What sits in the layers of a particular old building therefore depends strongly on its construction age and on later renovations.
Why lead is dangerous
Lead is a neurotoxin. It disrupts signal transmission and the development of the brain. Babies and children under about six are most strongly affected, because their nervous system is still developing and they absorb a considerably higher proportion of ingested lead than adults do; impairments of intelligence, attention and behaviour are described. In adults, the main concerns are high blood pressure and kidney damage. According to the WHO there is no safe threshold: even small amounts are considered harmful. The IARC of the WHO classifies inorganic lead compounds as probably carcinogenic (Group 2A) and metallic lead as possibly carcinogenic (Group 2B).
For experts (or the expert-curious): where the statement about the missing safe threshold comes from
The statement is not a formula of caution but the result of two reassessments made in 2010. The EFSA Panel on Contaminants in the Food Chain worked with the benchmark dose: one looks for the blood lead concentration associated with a pre-specified small effect and takes its lower one-sided 95 percent confidence bound as the reference point. For children's intelligence quotient the panel chose an effect of a single IQ point and arrived at a BMDL01 of 12 micrograms of lead per litre of blood; for systolic blood pressure in adults (effect 1.2 mmHg) at 36 µg/l, and for the prevalence of chronic kidney disease, where the chosen effect is 10 percent, at a BMDL10 of 15 µg/l. Its conclusion, verbatim: "The CONTAM Panel concluded that the current PTWI of 25 μg/kg b.w. is no longer appropriate as there is no evidence for a threshold for critical lead-induced effects" (EFSA CONTAM Panel 2010).
In June of the same year the Joint FAO/WHO Expert Committee on Food Additives, meeting in Geneva from 8 to 17 June 2010, reached the same result by the same route. It calculated that the provisional tolerable weekly intake of 25 micrograms per kilogram of body weight then in force corresponds to a loss of at least three IQ points in children and a rise in systolic blood pressure of about 3 mmHg in adults, withdrew it, and deliberately set no new one: "Because the dose–response analyses do not provide any indication of a threshold for the key effects of lead, the Committee concluded that it was not possible to establish a new PTWI that would be considered to be health protective" (JECFA, 73rd meeting, 2010).
The epidemiological basis is the same in both cases, and the FAO/WHO committee says so itself: the results of Lanphear et al. (2005) served it as the basis of the dose-response model, and that meta-analysis rests on the same studies as the EFSA analysis of 2010. It covers 1,333 children from seven longitudinal cohorts in the USA, Mexico, Kosovo and Australia, followed from birth or early infancy until the age of five to ten. Between 2.4 and 30 µg/dl of blood lead it found a decline of 6.9 IQ points (95 percent confidence interval 4.2 to 9.4). Broken down into steps, 3.9 of those points fall in the range from 2.4 to 10 µg/dl, 1.9 points from 10 to 20, and only 1.1 points from 20 to 30. The curve is therefore not merely without a threshold, it is steepest at the bottom: for children whose highest measured value was below 7.5 µg/dl, the loss per increment was significantly greater than for the others (Lanphear et al. 2005).
Two qualifications belong with this. First, EFSA and JECFA assess intake through food. Their anchor, however, is blood lead, and blood lead does not reveal whether it came from food, from water or from house dust; this is why the statement also holds inside a building. Second, the two bodies work in micrograms per litre, the WHO and the epidemiological literature in micrograms per decilitre: 12 µg/l is 1.2 µg/dl.
Recognising lead pipes
A lead pipe can be identified visually by several features: it is grey and matt, soft (a key easily leaves a notch, a fresh scratch gleams silver), sounds dull when tapped, is not magnetic, and the joints are bead-soldered rather than screwed. Such pipes are most likely found at the house connection in the basement, on the riser pipes and on the last metres under the sink or washbasin. Important: this is only the visual identification. How much lead actually passes into the water is told only by an analysis.
How to determine lead reliably
The lead content of paint, plaster or dust cannot be judged with the naked eye. The reliable method is laboratory analysis by an accredited laboratory. For drinking water the Austrian Drinking Water Ordinance prescribes the procedure for the compliance check: for copper, lead and nickel from building installations, one litre is taken at the consumer's tap without prior flushing, at a random time of day, the random daytime sample; if that sample exceeds the parameter value, a staggered sampling follows (TWV, Annex II Part C). For paint, plaster and solder joints, material samples are evaluated layer by layer, and for dust, wipe samples. Sampling it yourself is not advisable, especially with lead paint: anyone scratching or sanding suspect paint creates exactly the lead-containing dust they want to avoid. Such work, and the sampling, require expertise and protective measures.
For experts (or the expert-curious): what lead isotopes reveal, and where the method stops
Lead has four stable isotopes. The IUPAC Commission on Isotopic Abundances and Atomic Weights explains its ranges as follows: the atomic weight of lead is quite variable in nature because the three heaviest isotopes are the stable end-products of the radioactive decay of uranium and thorium, lead-206 from uranium-238, lead-207 from uranium-235 and lead-208 from thorium-232. How far that variation reaches is shown by the ranges of the amount fractions: for lead-206 from 0.0190 to 0.8673, for lead-208 from 0.0338 to 0.9775, while the non-radiogenic lead-204 lies between 0 and 0.0158. The same commission names both applications in one breath: the decay of uranium and thorium to lead permits geological age determinations, and the isotope-abundance variations enable historical and modern sources of lead to be identified (CIAAW).
Inside a building this does not mean that paint, pipe and street dust can simply be sorted out by their isotope ratios. How far the method carries there has been measured. In a nationwide French study, blood samples were taken from 125 children aged six months to six years with a blood lead level of 25 µg/l or more, and the candidate sources in their homes were sampled as well: dust, paint, soil, tap water and, where relevant, cosmetics. The lead isotope ratios were compared by way of their confidence intervals. A source counted as compatible, and thus as a suspected source, when its confidence interval overlapped that of the blood (Oulhote et al. 2011).
The result describes the reach of the method precisely. For 32 percent of the children a single suspected source remained; for 30 percent at least one source could be excluded as unlikely, which spares unnecessary removal work. The authors summarise it by saying that in France lead isotope ratios could provide valuable additional information in about a third of routine environmental investigations.
They name the limits just as clearly, and for practice those are the more important sentences. Sampling can never cover every route of intake, so the actual main source may be missing. A source can wrongly appear compatible if it carries the same signature as the real one, or if its signature lies between two real ones. Where several sources with different signatures act at once, the blood lies partway between them, and the real sources may then be considered incompatible. And blood carries not only freshly absorbed lead but also lead released from bone, with the signature of an exposure long past. Failure modes therefore run in both directions, and the authors do not say which of the two is the more reliable one. That is also the sensible role of provenance analysis in a building: it shortens the list of suspects, it does not replace the material sample.
The legal framework
The Austrian Drinking Water Ordinance sets the parameter value for lead at 5 µg/l (0.005 mg/l). For water under § 4 Z 1 and 3 of the ordinance that value must be met by 12 January 2036 at the latest; until then a parameter value of 10 µg/l (0.01 mg/l) applies there. Both values transpose the EU Drinking Water Directive (EU) 2020/2184. The directive does not stop at the value. Among the measures to reduce the risks arising from domestic distribution systems it lists, for lead, "if economically and technically feasible, implement measures for substitution of components made of lead in existing domestic distribution systems" (Article 10(3)(f)).
For experts (or the expert-curious): which water sample counts
A parameter value on its own does not yet say what is measured, and with lead that is the decisive half. The Austrian Drinking Water Ordinance lists lead in Annex I Part B at 5 µg/l with two notes. Note 4 refers to Annex II Part C for the procedure. Note 5 ties the transitional value to a scope: „Im Fall von Wasser gemäß § 4 Z 1 und 3 ist der Wert spätestens ab 12. Jänner 2036 einzuhalten. Bis dahin beträgt der Parameterwert für Blei 10 µg/l." (In the case of water under § 4 no. 1 and 3, the value must be met by 12 January 2036 at the latest; until then the parameter value for lead is 10 µg/l.) Section 4 no. 1 means the draw-off points of a distribution network normally used for taking water, no. 3 the water used in a food business. The transitional value therefore does not apply across the board but to these two cases.
Annex II Part C no. 2 describes the procedure, and it is not what one expects: „Proben zur Kontrolle der Einhaltung der chemischen Parameter Kupfer, Blei und Nickel in Wasser aus Gebäudeinstallationen werden ohne Vorlauf an der Entnahmestelle des Verbrauchers gezogen (Tageszufallsprobe). Zu einer zufälligen Tageszeit wird eine Probe von einem Liter Probenmenge entnommen. Bei Überschreitung eines Parameterwertes in der Tageszufallsprobe wird eine gestaffelte Probenahme durchgeführt." (Samples for checking compliance with the chemical parameters copper, lead and nickel in water from building installations are taken at the consumer's tap without prior flushing, as a random daytime sample of one litre at a random time of day; if a parameter value is exceeded, a staggered sampling is carried out.) The compliance sample is thus expressly not a stagnation sample with a prescribed standing time but a random sample without flushing; the staggered sampling follows only once that sample is conspicuous.
The directive behind it puts the matter the same way. Under Annex II Part D no. 2(a), "compliance samples for certain chemical parameters, in particular copper, lead, and nickel, shall be taken at the consumers' tap without prior flushing. A random daytime sample of one litre volume is to be taken. As an alternative, Member States may use fixed stagnation time methods that better reflect their national situation, such as the average weekly intake by consumers, provided that, at the supply zone level, this does not result in fewer cases of non-compliance than using the random daytime method". The average weekly intake appears there as an example of a national situation that an alternative method may reflect better, so the rationale belongs to the alternative and not to the default procedure; what share of actual intake a random daytime sample represents, the directive does not say. The Austrian transposition names the random daytime sample in Annex II Part C no. 2 and no method with a prescribed stagnation time.
A third point sits in the same note of the directive and explains why the reduction ends up affecting the domestic installation: "After that date, the parametric value of 5 μg/l shall be met at least at the point of supply to the domestic distribution system", and for the purposes of Article 11(2), which governs the approval of materials in contact with drinking water, "the parametric value of 5 μg/l at the tap shall apply". Whoever renovates only as far as the point of supply can spoil clean water again on the last stretch.
For the proper removal of lead-containing paints, the relevant occupational-safety and hazardous-substance rules apply. For old paint itself, by contrast, neither Austria nor Germany has a statutory threshold above which a coating counts as "lead paint" or as requiring remediation. That is a documented negative finding, not an oversight: a targeted search of the relevant bodies of law, in Austria the limit-value ordinance, health surveillance, chemicals and waste law, in Germany the hazardous-substances rules and the TRGS, finds no such value; a complete negative proof across the entire legal order cannot be produced, but the relevant regulations contain none. Other countries draw the line differently: the United States define "lead-based paint" from 0.5 percent by mass or 1.0 milligram per square centimetre (40 CFR 745.103); France sets the threshold for the "constat de risque d'exposition au plomb" at 1 milligram per square centimetre measured by X-ray fluorescence, or alternatively at 1.5 milligrams per gram of acid-soluble lead from laboratory analysis (Arrêté of 19 August 2011, Article 5). Which limits actually apply, where the frequently cited 0.3 percent comes from, and what a particular laboratory value means, is set out in detail in our article When is a coating lead paint?.
What to do
- Lead paint, intact: document and take into account at the next renovation. Do not sand, flame off or strip without protective measures. Painting over or sealing (encapsulation) is often the simplest solution.
- Lead paint, flaking, with children in the household: action needed. Professional removal or sealing by a specialist firm.
- Lead pipes: replacement is the only lasting solution; filters and coatings do not solve the problem. Until then the usual precautions apply: let the stagnation water run off until it comes cool from the tap (as the German Umweltbundesamt recommends), use only cold water for cooking and drinking (warm dissolves more lead), and no water from lead pipes for baby food. The same page gives the reason for letting it run: drinking water in older houses with lead pipes can show elevated lead levels, and this is particularly the case when the water has stood in the lead pipes for a longer time, for example overnight.
- Lead dust: wipe up damp rather than sweeping (sweeping spreads the dust), and eliminate the source.
Lead is not the only invisible pollutant in old buildings. Radon too can be neither seen nor smelled, and in buildings from before 1990 it is worth looking for asbestos.
Sources
- Drinking Water Ordinance (RIS), Annex I Part B (lead 5 µg/l, notes 4 and 5) and Annex II Part C no. 2 (random daytime sample): ris.bka.gv.at. Directive (EU) 2020/2184 on the quality of water intended for human consumption, OJ L 435, 23 December 2020, p. 1, Annex I Part B (lead 5 µg/l, 10 µg/l until 12 January 2036) and Annex II Part D no. 2(a) (sampling): eur-lex.europa.eu
- City of Vienna, "Blei im Trinkwasser" (lead installations mainly in Gründerzeit buildings constructed up to 1938; house-connection pipes replaced by 2007, in-apartment installations the owners' responsibility): wien.gv.at
- WHO, lead and health (no safe threshold, risk to children; in adults raised blood pressure and kidney damage): who.int. IARC: inorganic lead compounds Group 2A (Monograph Vol. 87, 2006), metallic lead Group 2B (Monograph Vol. 23/Supplement 7, 1987)
- No safe threshold, evidence base: EFSA CONTAM Panel, "Scientific Opinion on Lead in Food", EFSA Journal 2010;8(4):1570 (BMDL01 12 µg/l blood lead for developmental neurotoxicity, 36 µg/l for systolic blood pressure, BMDL10 15 µg/l for chronic kidney disease; PTWI of 25 µg/kg body weight no longer appropriate): doi.org/10.2903/j.efsa.2010.1570. JECFA, 73rd meeting, "Safety evaluation of certain food additives and contaminants", WHO Food Additives Series 64 (2011), Lead (addendum), section 10 (withdrawal of the PTWI, no new one possible): inchem.org. Lanphear, B. P. et al. (2005): Low-level environmental lead exposure and children's intellectual function: an international pooled analysis. Environmental Health Perspectives 113(7):894-899: PMC1257652
- Lead isotopes: Commission on Isotopic Abundances and Atomic Weights (IUPAC), "Lead" (isotope ranges; decay of uranium and thorium; age determination and source identification): ciaaw.org. Oulhote, Y. et al. (2011): Identification of sources of lead exposure in French children by lead isotope analysis: a cross-sectional study. Environmental Health 10:75: doi.org/10.1186/1476-069X-10-75
- German Environment Agency (UBA), „Blei im Trinkwasser ist gesundheitsgefährdend" (damage to the developing nervous system in children, impairment of blood formation and cognitive development, harmful even at very low intakes; elevated lead levels particularly after a longer standing time, for example overnight; recommendation to let the stagnation water run off until it comes cool from the tap): umweltbundesamt.de
- History of lead pigments: ILO Convention No. 13 "White Lead (Painting) Convention" (1921), ratified by Austria on 12 June 1924 (ILO NORMLEX); IARC Monographs Vol. 87 (2006, red lead as rust protection, lead chromate as yellow pigment); ColourLex, "Lead White"; present-day EU restriction REACH Regulation (EC) No 1907/2006, Annex XVII, entries 16 and 17
- Period of the bans and restrictions on lead white in interior painting (1905 to 1930, relayed there from the literature): van Driel, B. A., van den Berg, K. J., Gerretzen, J., Dik, J. (2018): The white of the 20th century: an explorative survey into Dutch modern art collections. Heritage Science 6, 16. doi.org/10.1186/s40494-018-0183-4
- France, Arrêté of 19 August 2011 on the "constat de risque d'exposition au plomb", Article 5 (1 mg/cm² by X-ray fluorescence, alternatively 1.5 mg/g acid-soluble lead; JORF no. 0202 of 1 September 2011, NOR ETSP1123269A): Légifrance JORFTEXT000024524952. US definition "lead-based paint" 40 CFR 745.103 (0.5 percent by mass or 1.0 mg/cm²): ecfr.gov
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