Lead Chromate Pigments Research Articles

Molybdenum doping leads to faster photo-dissolution of commercial molybdate red pigment than chrome yellow pigment under sunlight irradiation

The photo-dissolution of lead chromate pigments poses specific environmental hazards. In this study, we report that doping molybdenum in lead chromate pigments, resulting in commonly known molybdate red pigment, increases the risk of heavy metal leaching when exposed to light. Commercial molybdate red pigments undergo photo-dissolution when exposed to simulated sunlight and exhibit lower photostability compared to lead chromate pigments such as chrome yellow. After 24 h of irradiation, the leaching rates of toxic lead and chromium from molybdate red pigments were 2.98 and 3.70 times higher, respectively, than those from chrome yellow pigments. The primary factor leading to decreased pigment photostability is the activation of pigment semiconductors facilitated by molybdenum doping. Molybdate red pigments exhibit a broader light absorption spectrum and more efficient separation and transfer of photogenerated charge carriers than chrome yellow pigments, boosting the photochemical activity. To the best of our knowledge, this is the first study to illustrate the doping effect on the photostability of commercial inorganic pigments and the consequent heavy metal leaching. Our results suggest that Mo doping reduces the photostability of lead chromate pigments, highlighting the potential elevated environmental risks associated with complex inorganic pigments.

Effect of low molecular weight organic acids on the lead and chromium release from widely-used lead chromate pigments under sunlight irradiation

Lead chromate pigments are commonly used yellow inorganic pigments. They can pose environmental risks as they contain toxic heavy metals lead and chromium. Low molecular weight organic acids (LMWOAs), as widespread dissolved organic matter (DOM), affect the lead and chromium release from the pigment in water. In this work, the role of LMWOAs in the photodissolution of commercial lead chromate pigment was investigated. The pigment underwent significant photodissolution under simulated sunlight exposure with LMWOAs, and subsequently released Cr(III) and Pb(II). The photodissolution process is caused by the reduction of Cr(VI) by photogenerated electrons of the lead chromate pigment. The LMWOAs promoted photodissolution of the pigment by improving the electron-hole separation. The formation of Cr(III)-contained compounds leads to a slower release of chromium than lead. The photodissolution kinetics increase with decreasing pH and increasing LMWOAs concentration. The photodissolution of lead chromate pigment was basically positively related to the total number of hydroxyl and carboxyl groups in LMWOAs. The LMWOAs with stronger affinity to lead chromate pigment, lower adiabatic ionization potential (AIP) and higher energy of the highest occupied molecular orbital (EHOMO) are favorable to Cr(VI) reduction by photogenerated electrons and pigment photodissolution. 2.39% of chromium and 10.34% of lead released from the lead chromate pigment in natural conditions during a 6-h sunlight exposure. This study revealed the photodissolution mechanism of lead chromate pigment mediated by LMWOAs with different molecular structures, which helps understand the environmental photochemical behavior of the pigment. The present results emphasize the important role of DOM in the heavy metals release from commercial inorganic pigments.

Food safety policy enforcement and associated actions reduce lead chromate adulteration in turmeric across Bangladesh

Turmeric adulterated with lead chromate pigment has been previously identified as a primary source of lead exposure in Bangladesh. This study assesses the impact of a multi-faceted intervention between 2017 and 2021 to reduce lead-tainted turmeric in Bangladesh. The intervention involved: i) disseminating findings from scientific studies via news media that identified turmeric as a source of lead poisoning, ii) educating consumers and businesspeople about the risks of lead chromate in turmeric via public notices and face-to-face meetings, and iii) collaborating with the Bangladesh Food Safety Authority to utilize a rapid lead detection technology to enforce policy disallowing turmeric adulteration. Before and after the intervention, evidence of lead chromate turmeric adulteration was assessed at the nation's largest turmeric wholesale market and at turmeric polishing mills across the country. Blood lead levels of workers at two mills were also assessed. Forty-seven interviews were conducted with consumers, businesspeople, and government officials to assess changes in supply, demand, and regulatory capacity. The proportion of market turmeric samples containing detectable lead decreased from 47% pre-intervention in 2019 to 0% in 2021 (n = 631, p < 0.0001). The proportion of mills with direct evidence of lead chromate adulteration (pigment on-site) decreased from 30% pre-intervention in 2017 to 0% in 2021 (n = 33, p < 0.0001). Blood lead levels dropped a median of 30% (IQR: 21–43%), while the 90th percentile dropped 49% from 18.2 μg/dL to 9.2 μg/dL 16 months after the intervention (n = 15, p = 0.033). Media attention, credible information, rapid lead detection tools and swift government action to enforce penalties all contributed to the intervention's success. Subsequent efforts should evaluate if this is an example of an effective intervention that can be replicated to reduce lead chromate adulteration of spices globally.

A hybrid yellow nanopigment as an environmentally sound alternative to lead chromate pigment for pavement markings

This study entails the synthesis of a series of yellow hybrid dye-clay nanopigments (DCNPs) using different yellow cationic dyes, natural, and organomodified montmorillonite. The cationic exchange reaction served as a facile, one-pot, and low-temperature transformation strategy. DCNPs are explored as a type of lead-free eco-friendly pigment to substitute for conventional lead chromate pigment (PbCrO4) for pavement markings. The plate-like DCNP stacks with an approximate hydrodynamic diameter of 2.1 μm were well-dispersed in paint film, forming partially intercalated/exfoliated structure. DCNPs exhibited higher thermal stability, weathering stability, and chemical stability than PbCrO4. DCNPs featured the brilliant yellow shade in pavement marking paint, with the blue-yellow component value (b*) up to 69.9 units. The American pavement marking reference colors can be achieved with a considerably smaller amount of colorant when using DCNP, owing to its exceptional color strength. The cytotoxicity analysis revealed 91%, 66%, and 2% viability of fibroblast cells after a 48h treatment with 0.25 mg/ml natural DCNP, organoclay-based DCNP, and PbCrO4, respectively. In conclusion, the remarkable functional properties and low acute toxicity of the resulting nanopigments suggested the potential application of DCNP as a promising alternative to lead-based pigments in pavement markings.

Effects of accelerated aging on characteristics, leaching, and toxicity of commercial lead chromate pigmented microplastics

It is of environmental significance to study the leaching performance of additives from microplastics (MPs) and further evaluate the toxicity of leachate to microalgae. Here, we investigated the effects of accelerated aging on characteristics, leaching, and toxicity of commercial lead chromate pigmented MPs. Results show that aging of MPs caused surface cracks and fragmentation, increased their surface area and carbonyl contents, and promoted the release of lead chromate pigment. Chromium (Cr) and lead (Pb) tend to leach under acidic condition, rather than neutral and alkali environment. Aging treatment facilitates the leaching performance and a high concentration of NaCl solution also favors the leaching process. Toxicology experiments demonstrate that only high concentration of leachate (>10 μg L−1) exerted significant inhibitory influence (p < 0.005) on cell photosynthesis of Microcystis aeruginosa. The growth inhibition of algal cells remarkably increased with increasing leachate concentrations. We observed more inhibiting effects on cell growth and photosynthesis using the leachates of aged MPs. Longer aging time leads to more release of Cr and Pb, rendering higher toxicity to microalgae. These novel findings will benefit us from assessing the leaching behavior of additives in MPs and their toxicological risks to aquatic organisms.

Turmeric means “yellow” in Bengali: Lead chromate pigments added to turmeric threaten public health across Bangladesh

Adulteration is a growing food safety concern worldwide. Previous studies have implicated turmeric as a source of lead (Pb) exposure due to the addition of lead chromate (PbCrO4), a yellow pigment used to enhance brightness. We aimed to assess the practice of adding yellow pigments to turmeric and producer- consumer- and regulatory-factors affecting this practice across the supply chain in Bangladesh. We identified and visited the nine major turmeric-producing districts of Bangladesh as well as two districts with minimal turmeric production. In each district, we conducted semi-structured interviews and informal observations with individuals involved in the production, consumption, and regulation of turmeric. We explored perceptions of and preferences for turmeric quality. We collected samples of yellow pigments and turmeric from the most-frequented wholesale and retail markets. We collected samples of turmeric, pigments, dust, and soil from turmeric polishing mills to assess evidence of adulteration. Interviews were analyzed through an inductive, thematic coding process, with attention focused on perceptions of and preferences for turmeric quality. Samples were analyzed for Pb and chromium (Cr) concentrations via inductively coupled plasma mass spectrometry and x-ray fluorescence. In total, we interviewed 152 individuals from across the supply chain and collected 524 samples of turmeric, pigments, dust, and soil (Table S3, Table S4). Turmeric Pb and Cr concentrations were highest in Dhaka and Munshiganj districts, with maximum turmeric powder Pb concentrations of 1152 μg/g, compared to 690 μg/g in the 9 major turmeric-producing districts. We found evidence of PbCrO4-based yellow pigment adulteration in 7 of the 9 major turmeric-producing districts. Soil samples from polishing mills contained a maximum of 4257 μg/g Pb and yellow pigments contained 2–10% Pb by weight with an average Pb:Cr molar ratio of 1.3. Turmeric wholesalers reported that the practice of adding yellow pigments to dried turmeric root during polishing began more than 30 years ago and continues today, primarily driven by consumer preferences for colorful yellow curries. Farmers stated that merchants are able to sell otherwise poor-quality roots and increase their profits by asking polishers to adulterate with yellow pigments. Adulterating turmeric with lead chromate poses significant risks to human health and development. The results from this study indicate that PbCrO4 is being added to turmeric by polishers, who are unaware of its neurotoxic effects, in order to satisfy wholesalers who are driven by consumer demand for yellow roots. We recommend immediate intervention that engages turmeric producers and consumers to address this public health crisis and ensure a future with Pb-free turmeric.

Recycled electronic plastic and marine litter

Black consumer plastics are often contaminated with hazardous chemicals because of technological constraints on sorting dark plastic during recycling of municipal waste coupled with the convenience of waste electrical and electronic equipment (WEEE) as a secondary source of black plastic. In this study, samples of beached plastic litter (n = 524) from southwest England were categorised according to origin, appearance and colour (black versus non-black) before being analysed by x-ray fluorescence (XRF) spectrometry for elements that are characteristic of EEE. The small number of items of WEEE retrieved (n = 36) were largely restricted to wiring insulation and constructed of lead-stabilised polyvinyl chloride (PVC). Among the remaining samples, Br, Cd, Cr and Pb were commonly detected in all categories of black plastics (n = 264) with maximum concentrations of 43,400 mg kg−1, 2080 mg kg−1, 662 mg kg−1 and 23,800 mg kg−1, respectively. Moreover, concentrations of Br were significantly correlated with concentrations of the flame retardant synergist, Sb (n = 22), and 35 samples were potentially non-compliant with regard to limits defined by the Restriction of Hazardous Substances Directive. For plastics of other colours (n = 224), Br and Pb were detected in fewer samples and Br was co-associated with Sb in only two cases, with occasional high concentrations Cd, Cr and Pb largely attributed to the historical use of cadmium sulphide and lead chromate pigments. An avian physiologically-based extraction test applied to selected samples cut to mm-dimensions revealed bioaccessibilities ranging from <0.1% for Cr in a green fragment to about 2.4% (or about 580 mg kg−1) for Pb in black PVC. The recycling of WEEE into consumer, industrial and marine (e.g. fishing) plastics that are mainly coloured black appears to be an important vehicle for the introduction of hazardous chemicals into the environment and a source of their exposure to wildlife.

Was yellow lead chromate pigment used during Middle Stone Age at Sibudu rock shelter (South Africa)?

AbstractA recent study using the combination of optical microscopy and Raman spectroscopy revealed the presence of bright yellow residues of lead (II) chromate associated with grinding striations on a 58,000‐year‐old grindstone excavated at Sibudu rock shelter in South Africa. Lead (II) chromate (PbCrO4) exists in nature as the rare mineral crocoite, however was available as the synthetic pigment, chrome yellow, from the 19th century. At the time of the residue analysis on the grindstone, it was not possible to determine whether the yellow residues were due to modern contamination or a result of ancient use. Careful analyses of the excavation protocol followed at Sibudu rock shelter and all implements that might possibly have been in contact with the grindstone after excavation identified yellow spray paint as a possible origin of the contamination. Here, we performed experimental grinding of the mineral crocoite on a sandstone slab, sprayed yellow paint on rhyolite and compared optical microscopy and Raman spectroscopic analysis results to the archaeological sample. The optical appearance of the archaeological residues, the absence of associated minerals of crocoite, and the presence of organic matter mixed with lead chromate demonstrate that the residues on the archaeological grindstone stem from modern contamination. This paper draws attention to contamination issues originating from excavation practices.

Sunlight-Mediated Lead and Chromium Release from Commercial Lead Chromate Pigments in Aqueous Phase.

Lead chromate pigments are included in a group of the most widely used pigments, which account for 3% of worldwide lead consumption. This study reports the photoactivity of commercial lead chromate pigment (i.e., chrome yellow) under simulated sunlight. It underwent photodissolution in the presence of organic acid and dissolved organic matter in the aqueous phase, releasing Pb(II) and Cr(III). Pb(II) was released more readily than Cr(III) which mainly formed hydroxides and oxides. The photodissolution can be activated by light with a wavelength <514 nm. The reaction is mediated by the reduction of Cr(VI) in the pigment by self-generated electrons. The kinetics were mainly affected by the electron-hole separation efficiency which can be enhanced by electron donors. The reaction rate decreases with increasing solution pH as the photodissolution process consumes protons. The photodissolution of the chrome yellow pigment was further confirmed in a river water sample under natural sunlight, with 11.28% of lead and 2.56% of chromium released in 7 h. This study highlights the importance of considering photochemical processes in risk assessments and regulations of commercial semiconductor pigments, which are currently based on their solubility.

Nineteenth century chrome yellow and chrome deep from Winsor & NewtonTM

The Winsor & NewtonTM (W&N) nineteenth century archive database includes digitised images of hand-written instructions and workshop notes for the manufacture of their artists’ materials. For the first time, all 183 production records for yellow lead chromate pigments were studied and evaluated. They revealed that W&N produced essentially three pigment types: lemon/pale based on mixed crystals of lead chromate and lead sulphate [Pb(Cr,S)O4]; middle on pure monoclinic lead chromate [PbCrO4]; and deep that contains the latter admixed with basic lead chromate [Pb2CrO5]; accounting for 53, 22, and 21% of the production, respectively. Production records for primrose (4%) were also included since the formulation results in mixed crystals with a high percentage of lead sulphate, which, according to the literature, leaves it more prone to degradation. Each pigment type is characterised by only one or two main synthetic pathways; process variations reveal a systematic and thorough search for a high-quality durable product. A comparison of the chemical composition of pigment reconstructions with early W&N oil paint tubes showed that their records entitled ‘pale’ and ‘lemon’ correlated with the pigment in their tube labelled chrome yellow and, ‘middle’ and ‘deep’ with the label chrome deep. Lemon and middle pigment formulations were made into oil paints to assess their relative photo-stability. The degradation process was followed by colorimetry and was studied by synchrotron radiation-based techniques. Based on the X-ray absorption spectroscopy data, the possibility for creating a stability index for chrome yellows is discussed.

Analysis of 52 automotive coating samples for forensic purposes with Fourier transform infrared spectroscopy (FTIR) and Raman microscopy

ABSTRACTCompounds with Ti, Fe, Cu, Pb, and Cr are often added to coatings as pigments or additives. These heavy metals can be harmful to humans and result in contamination of soils, water, and sediments. Coatings, consisting of complex resins, pigments, and additives, are difficult to analyze. In this study, Fourier transform infrared spectroscopy (FTIR) and Raman microscopy were employed to investigate 52 coating samples with six different colors collected from everyday cases. Infrared has many advantages in identification of resins and additives, while Raman microscopy is more powerful in detecting additives and pigments. It is more effective using these two techniques in combination for identification than using them separately. Cu pigments were detected with high frequencies in blue and green samples; Ti was found in all white samples. Lead chromate pigment has been banned in the United States due to environmental concerns for more than 20 years. However, this pigment is still widely used in many other countries; its main substitute bismuth vanadate is not detected in all samples in this study. The result reveals that environmental scientists should seriously consider the potential ecological and health risks of Pb and Cr from the paints. The analysis of automotive coatings is also important for forensic scientists. Popular pigments, resins, and additives in the coatings are summarized in this study which can provide forensic scientists with helpful references in everyday cases.

Time to ban lead in industrial paints and coatings.

In the U.S. and most high-income countries, regulations already restrict the use of lead paint for residential applications. However, few countries have enacted comprehensive bans on the use of lead additives in all paints. In 2009, more than 120 countries at the UN International Conference on Chemicals Management (ICCM) voted to phase-out all lead paints (1). Since then, a few countries including the Philippines and Nepal have enacted regulations to eliminate the use of lead additives in both consumer and “industrial” paints, but most countries have no restrictions on the manufacture or use of lead in any type of paint (2). The hazards of lead paint have been known since at least the 1800s and even the recommended alternatives to lead pigments advocated in that era are still used in making paints today (3). Yet, the debate on banning lead paint still rages in capitols from Dhaka to Brussels despite overwhelming evidence that workers and children are harmed from lead exposures resulting from these applications. In the European Union (EU), a fight is currently under way over a petition to exempt Lead Chromate pigments from the registration, evaluation, authorization, and restriction of chemicals (REACH) regulations. It is an unusual battle that has pitted the world’s largest lead pigment manufacturer, the Canadian-based Dominion Colour Corporation, against some European industry associations and AkzoNobel, the world’s largest paint manufacturer, which eliminated the use of lead in all their products in 2011 (4, 5). Although in many countries, architectural/decorative paints still contain significant concentrations of lead, “industrial” paints generally have lead concentrations that are up to 10 times greater. For example, road marking paints can contain up to 20,000 ppm lead (6). However, there are well known substitutes for lead additives in all types of paints and coatings used for all applications. Despite the availability of substitutes, multi-national paint companies often sell lead-free coatings in some markets while they continue to market lead-containing products in jurisdictions where there are no regulatory constraints and customers are less aware of the hazards. In the U.S., efforts to regulate the lead content of paints initially focused on decorative/architectural paints and consumer products. Subsequently, large paint purchasers in the U.S. had begun to assess the costs of safely maintaining and eventual demolishing industrial structures, bridges, ships, and roadways with lead paint and elected to require lead-free paint and coatings in project and product specifications.

Correction: Synchrotron-based X-ray spectromicroscopy and electron paramagnetic resonance spectroscopy to investigate the redox properties of lead chromate pigments under the effect of visible light

Correction for ‘Synchrotron-based X-ray spectromicroscopy and electron paramagnetic resonance spectroscopy to investigate the redox properties of lead chromate pigments under the effect of visible light’ by Letizia Monico et al., J. Anal. At. Spectrom., 2015, 30, 1500–1510.

Synchrotron-based X-ray spectromicroscopy and electron paramagnetic resonance spectroscopy to investigate the redox properties of lead chromate pigments under the effect of visible light

The redox properties of chrome yellows under visible and monochromatic light exposure are studied using UV-vis, SR μ-XRF/μ-XANES and EPR spectroscopies.

Paper spray ionization for ambient inorganic analysis

The feasibility of using paper spray ionization as an ambient ionization method for inorganic analysis was investigated. Aqueous solutions were spotted onto paper triangles and high voltage was applied to induce electrospray. In-source collision-induced dissociation assisted in breaking up clusters to produce mass spectra dominated by atomic ions and their corresponding oxides and hydroxides and high-resolution exact mass measurements were used to identify atomic ions in the presence of organic interferences. A feasibility test with a standard inductively coupled plasma mass spectrometry (ICP-MS) test mixture demonstrated detection of 21 of 23 elements as M(+•) or [M + OH](+). The two undetected elements (boron and lithium) were below the minimum detectable m/z setting for the time-of-flight mass spectrometer used for these experiments. Untreated filter paper showed residual contamination from group I and group II elements. Excellent linearity was observed over the concentration range 0.1-1000 ppm for nickel(II) nitrate solutions containing 10 ppm cobalt(II) nitrate as internal standard. The method was applied to the analysis of lead-free solder, a bismuth subsalicylate tablet, permanent magnet materials and lead chromate pigment in a three-cent US postage stamp issued in 1948. Paper spray ionization was successfully applied to qualitative inorganic analysis. Quantitative analysis was shown to be possible with the use of internal standards. Initial detection limits were much higher than for comparable inductively coupled plasma and glow discharge methods, ranging from the high parts-per-billion range to the low parts-per-million range. The detection limits for some elements were limited at low levels by the presence of interferences that were not separated by the resolving power of the mass spectrometer. Despite these limitations, the simplicity and potential portability of paper spray may find some applications for elemental analysis.

BASF concentrates on alternatives to lead chromate pigments

BASF concentrates on alternatives to lead chromate pigments

BASF concentrates on alternatives to lead chromate pigments

BASF concentrates on alternatives to lead chromate pigments

Chromosome aberration test of Pigment Yellow 34 (lead chromate) in Chinese hamster ovary cells

Lead chromate pigment in the form of the commercial pigment, Pigment Yellow 34, CAS No. 1344-37-2, used in the plastics and coatings industries, did not induce chromosome aberrations in Chinese hamster ovary (CHO) cell line WB(L). Lead chromate pigment is essentially insoluble in water, and in an effort to test the material under realistic conditions, no attempt to solubilize the pigment was made. These results are significant because others have reported lead chromate to cause genotoxicity in various assays, but only under conditions in which its aqueous solubility was artificially enhanced.

Infrared Spectra of U.S. Automobile Original Finishes. VII. Extended Range FT‐IR and XRF Analyses of Inorganic Pigments In Situ—Nickel Titanate and Chrome Titanate

The identification, analysis, and occurrence in U.S. automobile original finishes (1974-1989) of Nickel Titanate (yellow) and Chrome Titanate (yellow-orange) are described in this report. The titanate pigments are based on the rutile (titanium dioxide) structure and there are only minor differences between the infrared absorptions of rutile and the titanates. Titanate pigment absorptions in paint spectra can thus be easily mistaken for those of rutile. Each of the titanates, however, contains two elements in addition to titanium that can serve to distinguish them using elemental analyses. Fourier transform infrared (4000-220 cm(-1)) and X-ray fluorescence instruments were used in combination for the in situ analysis of the titanates. In addition to titanium, nickel, and antimony, the three main detectable elements comprising Nickel Titanate, all of the commercial products of this pigment that were examined also contained impurities of zirconium, niobium, and usually lead. These elements were also detected in most of the monocoats in which Nickel Titanate was identified, as well as in the Chrome Titanate pigments, and the zirconium to niobium ratio was found to exhibit a wide variation. Nickel Titanate is a relatively common pigment that was identified in nearly three dozen U.S. automobile yellow nonmetallic monocoats (1974-1989), while Chrome Titanate appears to have been used in only a few yellow and orange nonmetallic monocoats. The use of the titanate pigments likely increased after this time period as they were replacements for lead chromate pigments (last used in a U.S. automobile original finish in the early 1990s), and are more amenable for use in basecoat/clearcoat finishes than in monocoats. Minor distortions of the infrared absorptions of rutile, anatase, and the titanates obtained using accessories with diamond windows were noted, and their origins are discussed.

Polymorph and Phase Discrimination of Lead Chromate Pigments by a Facile Room Temperature Precipitation Reaction

Monoclinic and orthorhombic PbCrO4, Pb2CrO5, and K2Pb(CrO4)2 nanocrystallites with different shapes can be selectively synthesized by a room temperature solution reaction without adding any additives. The results demonstrated that the manipulation of pH value and the molar ratio of Pb(Ac)2 and K2CrO4 can effectively affect the formation of polymorphs and phases. This facile room temperature approach provides a useful route for the selective synthesis of lead chromate pigments with different phases and polymorphs, a method which could be extended for other inorganic systems.