Lead, Cadmium and other metals in Residential Paint Chips from Indoor wall surfaces

doi:10.21203/rs.3.rs-3985756/v1

Paints beautify and shield houses, but may have risky metals like lead, cadmium, arsenic, and mercury that endanger occupants, mainly children and pregnant women. To assess the levels and health risks of 14 metals in paint chips from indoor walls of residential houses in four states in South-western Nigeria. Paint chips were collected from 144 houses with childrens’ occupants and analyzed for metals using inductively coupled plasma–optical emission spectrometer. The Cadmium (Cd) and Lead (Pb) levels (mg/kg) ranged from 1239.9-2254.2 and 1126.5- 3080.3 in all the states examined, respectively. Arsenic (As) ranged from 1236.3- 915.2 ± 4.800 and 972.5–1492.0 in Lagos and Ibadan, respectively. In Ado-Ekiti and Akure, the levels of As ranged 828.3- 920.4 and 822.1-842.3 mg/kg, respectively. The chronic daily intake, hazard quotient, hazard index, and lifetime cancer risk of metals were estimated for ingestion, inhalation, and dermal exposure routes. The concentrations of arsenic, cadmium, and lead in paint chips exceeded the permissible limits for paints. The highest metal exposure and health risk were through ingestion, followed by inhalation and dermal contact. Children had higher exposure and risk than adults. Arsenic had the highest hazard index and lifetime cancer risk among the metals, followed by lead, chromium, and cadmium. The study revealed that paint chips from indoor walls pose a significant source of metal contamination and health risk, especially for children. There is a need for stricter regulation and monitoring of metal content in paints and paint chips in Nigeria.

House scraps

Paints

Heavy metals

Health implications

Indoor air

Nigeri

Metal deposition and toxicity are experienced in indoor environment due to exposure to heavy metals (Tran et al., 2012; Tan et al., 2016) and have resulted in poor air quality (Tsakas et al., 2011; Tsakas and Siskos, 2011; Mitro et al., 2016). Settled airborne particles (≤ 100 µm) are referred to as indoor dust and are found in both interior and exterior sources (Darus et al., 2012; Faiz et al., 2012; Mitro et al., 2016; Tan et al., 2016). It may consist of consumer product chemicals, including many compounds with known or suspected health implications (Hassan, 2012; Tran et al., 2012; Huang et al., 2014; Praveena et al., 2015; Wang et al., 2015; Mitro et al., 2016).

Lead (Pb), Arsenic (As), Nickel (Ni), and Cadmium (Cd) plays no established biological functions, but are rather toxic anddisturb many biochemical and physiological processes in plants and animals, unlike zinc (Zn), copper (Cu), iron (Fe), and manganese (Mn) (Sardar et al., 2013; Jaishankar et al., 2014; Apanpa-Qasim et al., 2016; Apanpa-Qasim et al., 2017; Ali et al., 2019; Li et al., 2020). Metals have been a major concern and constant headache in our life time. Buildings are constantly designed by painting and repainting without considering questions like: (a) are paint hazardous? (b) at what level are they? (c) can we produce without endangering our health and the environment? Children are the most vulnerable to heavy metals from indoor dust as a result of crawling, hand-to-mouth activities, clinging of dust to body surface, inhalation of fine dust particles and fast growth rate (Sardar et al., 2013; Jaishankar et al., 2014; Latif et al., 2014; Olujimi et al., 2015; Hauptman et al., 2017).

Paints are consumer product known to be admired by most people and as a result, large surface areas when painted contributes chemical substances such as As, Cd, Cr, Cu, Hg, Ni, Pb, and Zn (Jaishankar et al., 2014; Apanpa-Qasim et al., 2016; Mitro et al., 2016; Apanpa-Qasim et al., 2017). These metals are in the priority pollutants list of EPA ( Dai et al., 2018; Derakhshan et al., 2018; Ali et al., 2019) and are capable of disrupting metabolic activities and genetic makeup, affect embryonic or foetal development, causing cancer, developmental disorders, and neurological and behavioural changes in children and vulnerable groups (Ali et al., 2013; Gore et al., 2015; Robinson et al., 2015; Nkwunonwo et al., 2020).

House scraps from paintings are chips which easily fall off over time from walls. House scraps can come from interior or exterior surfaces of a building. Exterior paint may also be removed by weathering process resulting to high Pb concentrations in runoff and waterways (Hauptman et al., 2017). The number of years the walls have been painted influence the extent of the deterioration of the paints (Hauptman et al., 2017).

Leaded paint concentrations often exceed 10,000 ppm in most developing and advanced countries (O'Connor et al., 2018). Despite Pb being an element of interest in most paint research work, very little information exist on other metals of great health and environmental interest (O'Connor et al., 2018). No doubt, painted wall surfaces are global threats to public health. Metals in paints remain a danger on reapplied painted walls for better aesthetics (Khan et al., 2021). There have been so many indoor dust studies in consumer products (Mitro et al., 2016; Shin et al., 2020; Araja et al., 2023; Nazzal et al., 2023). However, all of these past studies were more concerned in determining heavy metal composition in indoor dust which are mostly not related to paint chips.

This study examines 18 different houses that have been painted only once since the construction and have existed in the last 10 years and above with children occupants between 0–6 and above age range. This study specifications were carefully selected from a larger data collection during the cause of sampling. In order to fully explore the potential implications of heavy metals and metalloids in paint scraps from indoor wall surfaces, the following scientific questions were raised: a) Are the levels of heavy metals and metalloids in the paint chips of indoor wall surfaces toxic? b) Does the heavy metals in the paint chips of these indoor wall surfaces pose any form of health risk to humans? c) Does the age of these painted walls influence the levels of heavy metals and metalloids in the paint chips? This study has paucity of knowledge till date.

Sample Collection and pre-treatment

Paint chips samples were collected from indoor painted wall surfaces in four selected states in Southwestern Nigeria namely Ado-Ekiti, Akure, Lagos, and Ibadan. The paint chips were collected from residence painted into polythene bags by removing peeled paint chips from wall surfaces which have been reported by occupants in the indoor environment while cleaning. After collection, samples were preserved in an ice box (at 6 ^oC). Before the collection of samples, the polythene bags were treated with 10% nitric acid (Merck KGaA, Darmstadt, Germany), washed off using milli-Q water (Merck KGaA, Darmstadt, Germany), dried in a fume hood (CEM Corp., North Carolina, U.S.A) all night, and then covered with a foil. The samples were collected from 144 residences in duplicates and 18 samples were collected from each resident. Procedures adopted were according to United States Environmental Protection Agency guidelines (US EPA, 2001).

Sample preparation and digestion

Samples were prepared according to standard operating procedures for lead in paints (U.S. Consumer Product Safety Commission. (2009) with slight modification based on carefully optimized procedure by employing hotplate acid digestion method. The paint chips were ground into a fine powder using a porcelain pestle and mortar. Then, 0.50 g sample duplicates were weighed carefully into a 15-mL polypropylene centrifuge tube. About 10mLs of concentrated trace-metal–grade nitric acid (70% nitric acid) and 3mLs of 98% sulphuric acid were added to each sample in the Teflon vessels. A standing time was allowed to fully dissolve the samples. Samples were digested and vessels cooled. After sample mineralization, the digest was filtered with a Millipore filter membrane (Merck KGaA, Darmstadt, Germany) of 0.45 mm into a volumetric flask (Merck KGaA, Darmstadt, Germany). Then distilled water (25 mL) was added to the filtered sample.

Heavy metal analysis of paint chips digested samples

Digested samples were then analysed using Thermo scientific inductively coupled plasma–optical emission spectrometer Model iCAP 6300 duo coupled with an autosampler CETAC ASX-520, USA. The samples were measured for As, Al, Ni, Ti, Ca, Fe, Mg, Pb, Zn, Cd, Mn, Cu, Cr, Co at National Environmental Engineering Research Institute (NEERI) laboratory, Nehru Marg- Nagpur, Maharastra, India. Certified stock solutions (1000 mg/L) for each metal were used for the preparation of working standards from calibration standards of single elements (Merck KGaA, Darmstadt, Germany). During the preparation of working standards, 0.2% of HNO₃ (in the case of Cd and Pb) or 15% of HNO₃ (in the case of other metals) along with the Milli-Q water (Merck KGaA, Darmstadt, Germany) were used in the serial vol/vol dilution (using glass volumetric flask). The prepared working standards were then used to calibrate the equipment.

The quality of the analytical method used was d validated using the limit of detection (LOD), limit of quantification (LOQ), and recoveries. The calibration curve technique was used for metals quantification and the curves were derived from a plot between the standard solutions concentration and corresponding absorbance, which yielded linear regression values (R²) of 0.89 to 0.99 for all metals. The calibration curve data were used to determine the LOD as described by (Moosavi and Ghassabian, 2018). The recoveries of the heavy metals analysed ranged from 81.5–106%.

Statistical analysis

The data obtained for paint chips from indoor wall surfaces below 10 years old and those of 11 years and above were subjected to descriptive statistics (mean ± standard deviation). Independent t-test was used to determine the significant difference between the level of heavy metals between the paint chips from indoor wall surfaces below 10 years old and those of 11 years and above at 0.05 level of significance. All analyses were done using SPSS version 20.

Estimated health risk assessment

Inhalation, ingestion and dermal are major routes through which people are exposed to pollutants in the environment. In describing these three routes, an estimated health risk assessment model by the US Environmental Protection Agency can be used for its calculation (USEPA, 2001; Bamidele et al., 2020; Rabin et al., 2023). The calculated health risk assessment model not only describes these routes but also has values, which can be used to interpret data for children and adults.

Calculation

CDI_inhalation =\(\frac{C*Rinh*Fexp\times *Texp}{PBF*ABW*Tavg}\)

CDI_dermal =\(\frac{C*SAF*Askin*DAF*Fexp*Texp}{PBF*ABW*Tavg}\)

CDI_ingestion =\(\frac{C*Ring*Fexp*Texp*10⁻⁶}{ABW*Tavg}\)

HQ =\(\frac{CDI}{RfD}\)

And

HI =\(\sum _{k=1}^{n}{CDI}_{k}/{RfD}_{k}\)

Where CDI = chronic daily intake; C- exposure-point concentration: mg/kg; EF - exposure frequency: 180 days/years (Zheng et al, 2010a, b); ED - exposure duration: 30 years (USEPA, 2011); ET - exposure frequency: 24 hours/day (UDOE, 2011); AT - averaging time for carcinogens: 365 days/years × 70 years (USEPA, 2002); BW - body weight: 70 kg (adult), 15 kg (children) (USEPA, 1991); CF - units conversion factor: 10^− 6 kg/ mg (USEPA, 2002); SA — exposured skin area: 5700 cm²(USEPA, 2011); DAF is the dermal absorption factor (unitless) − 0.001 for both children and adults; PEF — particle emission factor: 1.36 × 10⁹ m³ kg^− 1(USEPA, 2002); CF—units conversion factor: 10^− 6 kg mg^− 1 (USEPA, 2002); R_ing -ingestion rate at 60 mg dust day^− 1 for children (1–6 years) and 30 mg day^− 1 for adults (USEPA, 2011); R_inh -inhalation rate at 20m³ day^− 1 for adults and 7.6m³ for children [24]; Fexp - exposure frequency, in this study, 180 day year-1 (Zheng et al, 2010a, b); T_exp is the exposure duration, 24 years for adults and 6 years for children (Van den Berg, 1995); A_skin is the skin area, in the study, 5700 cm² for adults and 2800 cm² for children (USEPA, 2001); Tavrg = Texp × 365 days is the averaging time for non-carcinogens.HQ - (non-cancer hazard quotient) - ratio of exposure to hazardous substances (Liu et al., 2013);

HI (chronic hazard index) - sum of more than one hazard quotient for multiple substances or multiple exposure pathways. HI values > 1 shows that there is a chance that non-carcinogenic risk may occur, and when HI < 1 the reverse implies.

The Incremental Lifetime Cancer Risk (ILCR) is calculated to know the probability of an individual developing cancer in his lifetime when exposed to potential carcinogens via the routes.

Incremental lifetime cancer risk = CDI_{(ing / inh / dermal)} × SLF, where SLF is the cancer slope factor

Total Lifetime Carcinogenic Risk is calculated by the addition of all the LCRs calculated for ingestion, inhalation and dermal.

TLCR = LCR_ingestion + LCR_inhalation + LCR_dermal

The tolerable or acceptable risk is in the range 10^− 6 – 10^− 4 (Liu et al., 2013; Rafiq et al.,2022) implying that if the range is exceeded, carcinogenic risk is most likely to occur over time.

Table 1 shows the concentrations of As, Cd, Cr, Pb and other metals used as pigments in paint chips of indoor wall surfaces harvested from Lagos, Ibadan, Ado-Ekiti and Akure. The concentration of As was significantly higher (p < 0.05) in paint chips of indoor wall surfaces below 10 years old from Lagos (1236.30 ± 5.90 mg/kg), while those of 11 years and above for Ibadan (1492.00 ± 4.80 mg/kg), Ado-Ekiti (920.40 ± 0.70 mg/kg), and Akure (842.3 ± 5.40 mg/kg) were significantly higher (p < 0.05). The concentration of Cd was significantly higher (p < 0.05) in paint chips of indoor wall surfaces below 10 years old from Lagos (1387.20 ± 9.60 mg/kg) and Akure (1876.90 ± 5.40 mg/kg), while those of 11 years and above for Ibadan (2254.20 ± 5.00 mg/kg) and Ado-Ekiti (1946.00 ± 7.50 mg/kg) were higher (p < 0.05). The concentration of Cr was significantly higher (p < 0.05) in paint chips of indoor wall surfaces of 11 years old and above from Lagos (15.60 ± 0.50 mg/kg), Ibadan (17.20 ± 1.10 mg/kg), Ado-Ekiti (22.40 ± 3.00 mg/kg), and Akure (60.6 ± 0.80 mg/kg). The concentration of Pb was significantly higher (p < 0.05) in paint chips of indoor wall surfaces of 11 years old and above from Lagos (1981.40 ± 9.00 mg/kg), Ibadan (2351.40 ± 8.40 mg/kg), Ado-Ekiti (3072.30 ± 6.90 mg/kg), and Akure (3080.30 ± 7.50 mg/kg). The ages of the peeling wall surfaces affected the levels of As (Ibadan, Ado-Ekiti, and Akure only), Cd (Ibadan and Ado-Ekiti only), Cr, and Pb, as the values were higher in older wall surfaces (11 years and above).

Table 1

Concentration of the studied metals in paint chips obtained
	ARPCO (years)	ARC	As	Cd	Cr	Pb	Al	Ca	Co	Cu	Fe	Mg	Mn	Ni	Ti	Zn
Lagos	˂10	0–5	1236.3 ± 5.9	1387.2 ± 9.6	7.2 ± 1.1	1141.7 ± 8.6	5332.5 ± 47.9	15479.0 ± 13.7	13.7 ± 0.5	643.2 ± 32.5	3343.7 ± 6.9	38437.1 ± 41.2	49.8 ± 0.5	136.2 ± 6.1	1864.5 ± 41.0	377.1 ± 6.4
	˃11	˃6	915.2 ± 4.8	1329.5 ± 8.5	15.6 ± 0.5	1981.4 ± 9.0	6136.6 ± 9.3	9363.1 ± 38	16.0 ± 0.7	449.2 ± 2.9	2762.1 ± 23.1	42693.2 ± 6.2	151.3 ± 1.3	139.9 ± 6.6	3510.7 ± 25.5	285.2 ± 0.7
Ibadan	˂10	0–5	972.5 ± 7.8	1324.2 ± 8.4	2.5 ± 0.7	2187.1 ± 4.8	7199.4 ± 3.9	7171.1 ± 56.5	32.8 ± 3.0	198.1 ± 1.1	733.6 ± 13.4	19892.8 ± 19.2	146.6 ± 9.1	168.1 ± 0.0	3177.2 ± 49.5	384.8 ± 2.7
	˃11	˃6	1492.0 ± 4.8	2254.2 ± 5.0	17.2 ± 1.1	2351.4 ± 8.4	17697.7 ± 4.8	5869.5 ± 17.3	26.8 ± 1.8	760.3 ± 2.4	720.6 ± 2.4	36932.3 ± 18.7	96.3V1.7	116.9 ± 4.5	3273.4 ± 66.1	108.6 ± 2.3
Ado-Ekiti	˂10	0–5	828.3 ± 1.6	1831.6 ± 1.7	19.8 ± 0.8	1126.5 ± 1.0	9105.7 ± 13.6	10511.3 ± 11.1	29.1 ± 0.9	760.7 ± 23.6	4299.8 ± 25.2	38454.6 ± 63.1	57.9 ± 3.2	111.5 ± 7.0	2946.9 ± 38.1	90.9 ± 5.7
	˃11	˃6	920.4 ± 0.7	1946.0 ± 7.5	22.4 ± 3.0	3072 ± 6.9	79687.6 ± 16.1	15536.0 ± 6.7	45.1 ± 7.1	750.7 ± 13.9	7187.1 ± 17.2	29797.4 ± 19.6	54.4 ± 5.4	95.0 ± 7.1	4254.8 ± 47.9	109.3 ± 19.2
Akure	˂10	0–5	822.1 ± 6.4	1876.9 ± 5.4	17.3 ± 0.6	2997.8 ± 3.9	17785.6 ± 4.9	5296.5 ± 17.6	15.7 ± 1.9	367.8 ± 1.4	2508.8 ± 15.4	27767.8 ± 16.5	218.1 ± 1.9	100.7 ± 1.1	4188.0 ± 27.2	135.4 ± 4.7
	˃11	˃6	842.3 ± 5.4	1239.9 ± 9.1	60.6 ± 0.8	3080.3 ± 7.5	8994.1 ± 783	8286.9 ± 78.3	13.7 ± 0.9	203.8 ± 4.7	6136.3 ± 2.2	28584.3 ± 32.5	119.2 ± 1.6	129.0 ± 0.3	3183.5 ± 18.4	176.9 ± 1.5
ARPCO = Age range of paint chips obtained (years)

For other metals examined, the concentration of Al was significantly higher (p < 0.05) in paint chips obtained from wall surfaces below 10 years old from Lagos (5332.5 ± 47.90 mg/kg), while those obtained from 11 years and above wall surfaces for Ibadan (17697.7 ± 4.80 mg/kg), Ado-Ekiti (79687.6 ± 16.1 mg/kg), and Akure (8994.1 ± 5.0 mg/kg) were significantly higher (p < 0.05). The concentration of Ca was significantly higher (p < 0.05) in paint chips obtained from indoor wall surfaces below 10 years old from Lagos (15479.0 ± 13.7 mg/kg) and Akure (5296.5 ± 17.4 mg/kg), while those of 11 years and above for Ibadan (5869.5 ± 17.3 mg/kg) and Ado-Ekiti (15536.0 ± 6.7 mg/kg) were higher (p < 0.05). The concentration of Co was significantly higher (p < 0.05) in paint chips obtained from indoor wall surfaces of 11 years old and above from Lagos (16.0 ± 0.7 mg/kg), Ibadan (26.8 ± 1.8 mg/kg), Ado-Ekiti (45.1 ± 7.1 mg/kg), and Akure (13.7 ± 0.9 mg/kg). The concentration of Cu was significantly higher (p < 0.05) in paint chips obtained from indoor wall surfaces of 11 years old and above from Lagos (449.2 ± 2.9 mg/kg), Ibadan (760.3 ± 10.1 mg/kg), Ado-Ekiti (750.7 ± 13.9 mg/kg), and Akure (203.8 ± 4.7 mg/kg). The concentration of Fe was significantly higher (p < 0.05) in paint chips obtained from indoor wall surfaces below 10 years old from Lagos (3343.7 ± 6.9 mg/kg), while those of 11 years and above for Ibadan (720.6 ± 2.4 mg/kg), Ado-Ekiti (7187 .4 ± 17.2 mg/kg), and Akure (6136.3 ± 2.2 mg/kg) were significantly higher (p < 0.05). The concentration of Mg was significantly higher (p < 0.05) in paint chips obtained from indoor wall surfaces below 10 years old from Lagos (38437.1 ± 41.2 mg/kg) and Akure (27767.8 ± 16.5 mg/kg), while those of 11 years and above for Ibadan (36932.3 ± 18.7 mg/kg) and Ado-Ekiti (29797.4 ± 19.6 mg/kg) were higher (p < 0.05).

The age range of paint chips obtained affected the levels of Mn (Lagos only), Ni (Lagos and Akure only), Ti (in all the states except Akure), and Zn (Ado-Ekiti and Akure), as the values were higher in older wall surfaces (11 years and above). The concentrations of EU priority metals (As, Cd, Pb) were above their permissible limits of 25 mg/kg, 100 mg/kg and 90 mg/kg in paints, respectively except chromium, which was 78% below permissible limit of 60 mg/kg. As a result, of the painted walls is fit for residences. The heavy metal concentrations in the chips samples varied depending on the location of the sampling points and the sources of contamination (Ogilo et al., 2017). The presence of heavy metals in paints and indoor dust poses potential health risks, particularly to young children who may be more susceptible to exposure. Lead, in particular, can have pronounced negative effects on children, impacting neurodevelopment and leading to behavioural problems. Other heavy metals such as cadmium, chromium, and zinc also pose health risks, including respiratory, cardiovascular, and gastrointestinal issues, especially at elevated levels (Tan et al., 2016; Abdulraheem et al., 2022).

Non-carcinogenic risks (hazard quotient) of metal exposure

The chronic daily intake of metals of exposure to house scraps via ingestion was highest among the routes, followed by inhalation and dermal in both children and adults. For the non-carcinogenic risk, ingestion appears to be the main exposure route followed by inhalation, then dermal contact for both adult and children. Children still get involved with the hand to mouth contact at the slightest opportunity while growing up apart from the fact that metals can contaminate their food, surfaces of the home during daily activities such as dusting and sweeping. This can introduce indoor dust particles. Hence, ingestion is the main exposure route of toxic metals by children as they like to play on the floor of the house and indirectly ingest it aside inhalation and skin contact (Olujimi et al., 2015; Apanpa-Qasim, 2016; Nduka et al., 2019; Bamidele et al., 2020). The non-carcinogenic risk (hazard quotient) followed the order As > Pb > Cr > Cu > Ni > Zn for inhalation and dermal routes in adults and children, As > Cd > Pb > Cr > Cu > Ni > Al > Zn > Mn for ingestion in adults and children (Table 2–3). Arsenic has the highest metal of exposure in all the routes of exposures

Table 2

Non-carcinogenic risks (Hazard Quotient) of metal exposure for adult
		Inhalation Adult						Ingestion Adult						Dermal Adult
States	ARPCIW	As	Cr	Pb	Cu	Ni	Zn	As	Cr	Pb	Cu	Ni	Zn	As	Cr	Pb	Cu	Ni	Zn
Lag	˂10	4.26E-04	2.61E-05	3.36E-05	1.66E-06	6.85E-07	1.30E-07	8.71E-01	5.07E-04	6.89E-02	3.40E-03	1.44E-03	2.66E-04	2.08E-05	2.48E-07	4.49E-06	1.11E-08	5.21E-08	1.30E-08
	˃11	3.15E-04	5.65E-05	5.87E-05	1.16E-06	7.25E-07	9.85E-08	1.57E + 00	5.50E-02	7.98E-01	7.91E-03	5.48E-03	1.00E-03	1.54E-05	5.37E–07	7.80E-06	7.74E-08	5.35E-08	9.82E-09
Iba	˂10	3.36E-04	9.06E-06	4.32E-04	1.71E-06	2.09E-05	6.64E-07	6.85E-01	1.06E-06	9.24E-04	1.05E-03	2.09E-05	2.71E-04	1.63E-05	8.61E-06	8.61E-06	3.41E-08	6.43E-08	1.33E-08
	˃11	1.26E-03	6.23E-05	4.87E-07	1.96E-06	1.24E-03	3.75E-08	2.56E + 00	1.21E-03	1.24E-02	1.32E-02	1.24E-03	3.83E-04	2.51E-05	5.93E-07	9.26E-06	1.31E-07	4.47E-08	3.74E-09
Ado-Ekiti	˂10	2.85E-04	7.17E-05	3.32E-05	1.97E-06	5.78E-07	3.14E-08	5.84E-01	6.97E-02	1.98E-02	4.02E-03	4.36E-03	6.40E-05	1.39E-05	6.82E-07	4.43E-06	1.31E-07	4.27E-08	3.13E-09
	˃11	3.81E-04	8.11E-05	9.04E-05	1.93E-06	1.82E-06	1.89E-07	1.58E-+00	1.58E-03	1.62E-02	1.32E-02	1.18E-05	3.85E-04	1.55E-05	7.72E-07	1.21E-05	1.29E-07	3.64E-08	3.77E-09
Akure	˂10	6.92E-04	6.27E-05	8.82E-05	9.53E-07	6.14E-09	4.68E-08	5.79E-01	6.09E-02	5.28E-02	1.94E-03	1.06E-03	9.54E-05	1.38E-05	5.96E-07	1.18E-05	6.33E-08	3.85E-08	4.66E-09
	˃11	2.90E-04	2.20E-04	9.07E-05	1.76E-06	6.49E-06	6.11E-08	1.45E-+00	2.56E-05	1.63E-02	3.59E-03	1.36E-03	6.23E-03	1.42E-05	2.09E-06	1.21E-05	3.51E-08	4.94E-09	6.09E + 09

ARPCIW = Age range of paint chips obtained in walls

Table 3

Non-carcinogenic risks (Hazard Quotient) of metal exposure for Children
		Inhalation children						ingestion children						Dermal children
State	ARPCOW	As	Cr	Pb	Cu	Ni	Zn	As	Cr	Pb	Cu	Ni	Zn	As	Cr	Pb	Cu		Ni	Zn
Lagos	˂10	1.89E-04	1.16E-05	1.49E-05	7.35E-07	3.04E-07	5.77E-08	8.13E + 00	4.73E-03	6.43E-01	3.17E-02	1.34E-02	2.48E-03	3.40E-05	4.06E-07	7.36E-06	1.81E-07		8.54E-08	2.13E-08
	˃11	1.40E-04	2.39E-07	2.60E-05	5.16E-07	3.21E-07	4.37E-08	1.47E + 01	1.03E-02	7.44E + 00	2.22E-02	5.11E-02	9.38E-03	2.52E-05	8.80E-07	1.28E-05	1.27E-07	8.77E-08		1.61E-08
Ibadan	˂10	3.63E-04	1.91E-06	1.91E-04	7.58E-07	1.43E-06	2.95E-07	6.39E + 00	1.64E-03	8.63E-03	3.26E-02	1.95E-04	2.53E-03	2.68E-05	1.41E-07	1.41E-05	5.59E-08		1.05E-07	6.13E-09
	˃11	2.28E-04	2.76E-05	3.07E-05	8.69E-07	2.61E-07	1.66E-08	9.81E + 00	1.13E-02	1.33E + 00	3.75E-02	1.15E-02	7.14E-04	4.11E-05	9.70E-07	1.52E-05	2.14E-07		7.33E-08	6.13E-09
Ado-Ekiti	˂10	1.27E-04	3.03E-07	1.48E-05	8.73E-07	2.56E-07	1.39E-08	5.45E + 00	6.51E-01	6.35E-01	1.25E-01	1.10E-02	5.98E-04	8.24E-05	1.12E-06	7.26E-06	2.15E-07		6.99E-08	5.13E-09
	˃11	3.44E-04	1.71E-05	2.69E-04	2.87E-06	8.08E-07	8.37E-08	6.05E + 00	8.84E-05	1.73E + 00	3.70E-02	9.37E-03	7.19E-04	1.24E-04	1.26E-06	1.98E-05	2.12E-07		5.95E-08	6.17E-09
Akure	˂10	1.25E-04	2.78E-05	3.91E-05	4.20E-07	2.72E-09	2.07E-08	1.32E + 01	1.14E-02	1.13E + 01	1.81E-02	3.68E-02	8.90E-04	1.04E-04	9.76E-07	1.93E-05	1.04E-07		6.31E-08	7.64E-09
	˃11	1.29E-04	9.28E-07	4.04E-05	2.34E-07	2.88E-07	2.71E-08	5.54E + 00	3.98E-02	1.74E + 00	3.35E-02	1.50E-04	1.16E-03	6.94E-05	3.42E-06	1.99E-05	5.75E-08		8.08E-08	9.98E-09

ARPCIW = Age range of paint chips obtained in walls (years)

followed by lead for both adults and children. These findings are consistent with other studies that have reported high levels of heavy metals in indoor dust and paint chips, and their potential health risks to the occupants, especially children and pregnant women (Lin et al., 2015; Chem et al., 2023; Soltanpour et al., 2023). Heavy metals in indoor environments can originate from various sources, such as interior paint, metal objects, building materials, vehicle emissions, and soil (Lin et al., 2015). Exposure to these metals can cause various adverse effects, such as neurotoxicity, nephrotoxicity, immunotoxicity, and carcinogenicity (Chen et al., 2023). Hence, the findings highlights the need for stricter regulation and monitoring of metal content in paints and paint chips in Nigeria, as well as the implementation of preventive exposure control measures, such as local ventilation, personal protective equipment, and regular cleaning (Chen et al., 2023). By doing so, the health risks of heavy metals in indoor environments can be reduced and the quality of life of the occupants can be improved.

Hazard indexes for metals exposure (HI)

The hazard index for metal exposure to children and adult are presented in Table 4, arsenic has the highest metal exposure in the hazard index (HI for adults and children). The order followed As > Pb > Cr > Cu > Ni > Zn in all metal examined for both adults and children. Arsenic was a bit higher in adults than children. Lead exposure was highest in children than adults in 25 fold. The highest route of exposure is via ingestion. Indoor dust can be contaminated with paints by paint fall off, repainting process etc. During the daily sweeping of the houses, residents can equally be exposed to paint scraps from walls around the home (Beauchemin et al., 2011). In this study, it was observed that arsenic showed a HI value higher than 1 which implies cancer risk is possible. HI > 1 was observed in arsenic values of 1.573(1.57E + 00), 2.563 (2.56E + 00), 1.581 (1.58E + 00), 1.447 (1.45E + 00) via ingestion exposure routes as shown in Table 6, from wall surfaces of 11 years and

Table 4

Hazard indexes for metals exposure in Adults and Children
		As		Cr		Pb		Cu		Ni		Zn
State	ARPCO IDWS	Adult	Children	Adult	children	Adult	children	Adult	children	Adult	children	Adult	children
Lagos	˂10	0.871421	8.129319	0.000534	0.004746	0.068981	0.643485	0.0034	0.03172	0.00144	0.013434	0.000266	0.00248
	˃11	1.572914	14.67761	0.055008	0.010259	0.797723	7.444829	0.007913	0.022153	0.005476	0.051105	0.001005	0.009376
Ibadan	˂10	0.685479	6.39491	0.000012	0.001646	0.001365	0.008834	0.001048	0.032565	0.000024	0.000197	0.000272	0.00253
	˃11	2.564978	9.81068	0.001275	0.011338	0.012434	1.325297	0.013393	0.037495	0.001236	0.01153	0.000383	0.000714
Ado-Ekiti	˂10	0.583837	5.446565	0.069818	0.65096	0.019878	0.634918	0.004021	0.125048	0.004365	0.010998	0.000064	0.000598
	˃11	1.581852	6.052413	0.00166	0.000107	0.016336	1.731839	0.013224	0.037024	0.000014	0.009371	0.000385	0.000719
Akure	˂10	0.579877	13.18459	0.061003	0.011404	0.052899	11.26381	0.001944	0.018139	0.001064	0.036785	0.000095	0.00089
	˃11	1.447624	5.538609	0.000247	0.039851	0.016378	1.73612	0.003591	0.033502	0.001364	0.00015	0.000623	0.001163

ARPCOID = Age range obtained in indoor wall surface (years)

above where adults, 6 years and above children reside from Lagos, Ibadan, Ado-Ekiti, Akure, respectively. There could be a possible cancer risk to children (Iwasaki et al., 2023). Exposure to inorganic arsenic compounds, which are more toxic than organic arsenic compounds, can cause various adverse effects, such as skin lesions, pigmentation changes, hyperkeratosis, peripheral neuropathy, cardiovascular diseases, diabetes, and cancer (Inoue et al., 2022; Iwasaki et al., 2023). The International Agency for Research on Cancer (IARC, 2012) has classified inorganic arsenic as a human carcinogen, and has linked it to increased risk of lung, bladder, skin, liver, and kidney cancers.

Life time cancer risk assessment

Tables 5 and 6 showed the lifetime cancer risk in adults and children, respectively. LCR is a measure of how likely a person is to develop cancer over their lifetime (usually 70 years) from a given pollutant concentration and intake level (Tran et al., 2016). The Lifetime Carcinogenic risk in children and adults across all heavy metals studied ranged from LCR_ingestion> LCRi_nhalation >LCR_dermal. From this study, these metals are harmful as they enter the body through the digestive system than through the respiratory system or the skin (Troudi et al., 2022) who reported the LCRs of heavy metals in water through ingestion and dermal contact were higher for children than for adults, and higher for As, Cd, and Cr than for other metals. The study also found that the LCRs of heavy metals in water ranged from LCR (ing) > LCR (inhalation) > LCR (dermal), meaning that ingestion was the most significant exposure pathway, followed by inhalation and dermal contact. A review by Tan et al., (2016) also confirmed that ingestion was the main exposure route for children, and that the LCRs for As, Cd, Cr, and Pb.

Table 5

Lifetime Cancer Risk Values for metals exposure in adults
		Inhalation –Adult							Ingestion- Adult
	ARPCOIWS	Cd	Cr	Pb	Mn	Ni	Zn	Cd Cr		Pb	Mn	Ni	Zn	Cd	Cr Pb		Mn		Ni	Zn
Lagos	˂10	5.46E-08	3.73E-10	5.91E-08	0	2.40E-08	0	1.11E-04	7.61E-07	1.21E-04	0	4.89E-05	0	1.09E-09	7.44E-12	1.18E-09	0	4.79E-10		0
	˃11	5.23E-08	8.08E-10	1.03E-07	0	2.46E-08	0	1.07E-04	1.65E-06	2.09E-04	0	5.03E-05	0	1.04E-09	1.61E-11	2.05E-09	0		4.92E-10	0
Ibadan	˂10	5.21E-08	1.30E-10	1.13E-07	0	2.96E-08	0	1.06E-04	2.64E-07	2.31E-04	0	6.04E-05	0	1.04E-09	2.58E-12	2.26E-09	0	5.91E-10		0
	˃11	8.87E-08	8.91E-10	1.22E-07	0	2.06E-08	0	1.81E-04	1.82E-06	2.48E-04	0	4.20E-05	0	1.77E-09	1.78E-11	2.43E-09	0	4.11E-10		0
Ado-Ekiti	˂10	7.21E-08	1.03E-09	5.84E-08	0	1.96E-08	0	1.47E-04	2.09E-06	1.19E-04	0	4.01E-05	0	1.44E-09	2.05E-11	1.16E-09	0	3.92E-10		0
	˃11	7.66E-08	1.16E-09	1.59E-07	0	1.67E-08	0	1.56E-04	2.37E-06	3.25E-04	0	3.41E-05	0	1.53E-09	2.31E-11	3.18E-09	0	3.34E-10		0
Akure	˂10	7.39E-08	8.96E-10	1.55E-07	0	1.77E-08	0	1.51E-04	1.83E-06	3.17E-04	0	3.62E-05	0	1.47E-09	1.79E-11	3.10E-09	0	3.54E-10		0
	˃11	4.88E-08	3.14E-09	1.60E-07	0	2.27E-08	0	9.96E-05	6.40E-06	3.26E-04	0	4.63E-05	0	9.74E-10	6.26E-11	3.18E-09	0	4.53E-10		0

ARPCOIWS = Age range of paint chips obtained in indoor wall surfaces (years)

Table 6

Lifetime Cancer Risk Values for metals exposure in Children
		Inhalation-Children						ingestion -children						Dermal-Children
State	ARPCOIWS	Cd	Cr	Pb	Mn	Ni	Zn	Cd	Cr	Pb	Mn	Ni	Zn	Cd	Cr	Pb	Mn	Ni	Zn
Lagos	˂10	2.42E-08	1.65E-10	2.62E-08	0	1.06E-08	0	1.04E-03	7.10E-06	1.13E-03	0	4.57E-04	0	1.78E-09	1.22E-11	1.93E-09	0	7.84E-10	0
	˃11	2.32E-08	3.58E-10	4.55E-08	0	1.09E-08	0	9.97E-04	1.54E-05	1.95E-03	0	4.69E-04	0	1.71E-09	2.64E-11	3.35E-09	0	8.05E-10	0
Ibadan	˂10	2.31E-08	5.74E-11	5.02E-08	0	1.31E-08	0	9.93E-04	2.47E-06	2.16E-03	0	5.64E-04	0	1.70E-09	4.23E-12	3.70E-09	0	9.67E-10	0
	˃11	3.93E-08	3.95E-10	5.40E-08	0	9.13E-09	0	1.69E-03	1.70E-05	2.32E-03	0	3.92E-04	0	2.90E-09	2.91E-11	3.98E-09	0	6.73E-10	0
Ado-Ekiti	˂10	3.20E-08	4.55E-10	2.59E-08	0	8.71E-09	0	1.37E-03	1.95E-05	1.11E-03	0	3.74E-04	0	2.36E-09	3.35E-11	1.91E-09	0	6.42E-10	0
	˃11	3.40E-08	5.14E-10	7.06E-08	0	7.42E-09	0	1.46E-03	2.21E-05	3.03E-03	0	3.19E-04	0	2.50E-09	3.79E-11	5.20E-09	0	5.47E-10	0
Akure	˂10	3.28E-08	3.97E-10	6.88E-08	0	7.86E-09	0	1.41E-03	1.71E-05	2.96E-03	0	3.38E-04	0	2.41E-09	2.93E-11	5.07E-09	0	5.79E-10	0
	˃11	2.16E-08	1.39E-09	7.07E-08	0	1.01E-08	0	9.29E-04	5.98E-05	3.04E-03	0	4.33E-04	0	1.59E-09	1.03E-10	5.21E-09	0	7.42E-10

ARPCOIWS = Age range of paint chips obtained in indoor wall surfaces (years)

Total Lifetime Cancer Risk Values for metals exposure in adults (TLCR)

The TLCR values obtained in this study for both children and adult is presented in Table 7. TLCR stands for total lifetime cancer risk, which is a measure of the probability of developing cancer over a lifetime due to exposure to a carcinogen (Alghamdi et al., 2019; Nduka et al., 2019; Li et al., 2021; Xu et al., 2022;). The acceptable level of risk for TLCR value varies depending on the context and the regulatory agency, but a common range is between 1 × 10 − 6 and 1 × 10 − 4 (Al Osman et al., 2019; Cai et al.,2019). The highest TLCR value obtained in this study for the selected metals in both adults and children in the order Pb > Cd > Ni > Cr. This implies that a high cancer risk for both adults and children exist in these four metals in this order. From the study, the highest TLCR value for lead in children was 3.04E-03 and the lowest TLCR for lead in children was 1.11E-03 while the highest TLCR for lead in adult was 3.26E-04 and the lowest TLCR for lead in adult was 1.19E-04. This is followed by the highest TLCR for cadmium in children was 1.69E-03 and the lowest TLCR for lead in children was 9.29E-04 while the highest TLCR for cadmium in adult was 1.81E-04 and the lowest TLCR for cadmium in adult was 9.96E-05; followed by the highest TLCR value for nickel in children was 5.64E-04 and the lowest TLCR for nickel in children was 3.19E-04 while the highest TLCR for nickel in adults was 6.04E-05 and the lowest TLCR for nickel in adult was 3.42E-05 and the highest TLCR value for chromium in children was 5.98E-05 and the lowest TLCR for nickel in children was 2.47E-06 while the highest TLCR for nickel in adults was 6.41E-06 and the lowest TLCR for nickel in adult was 2.64E-07. The TLCR for children were among the limit (1x10^− 6 – 1x10^− 4) given by USEPA (2001) in all the values of cadmium and lead.

Therefore, paint chips poses a serious health risk for both children and adults. Young children, less than 6 years old, are population at high risk for lead poisoning apart from other metals examined because

Table 7

Total Lifetime Cancer Risk Values for Cd, Cr, Pb, Mn, Ni, Zn
		Adult						Children
States	ARPCOIWS	Cd	Cr	Pb	Mn	Ni	Zn	Cd	Cr	Pb	Mn	Ni	Zn
Lagos	below 10	1.11E-04	7.61E-07	1.21E-04	0.00E + 00	4.90E-05	0.00E + 00	1.04E-03	7.10E-06	1.13E-03	0.00E + 00	4.57E-04	0.00E + 00
	11 & above	1.07E-04	1.65E-06	2.09E-04	0.00E + 00	5.03E-05	0.00E + 00	9.97E-04	1.54E-05	1.95E-03	0.00E + 00	4.69E-04	0.00E + 00
Ibadan	below 10	1.06E-04	2.64E-07	2.31E-04	0.00E + 00	6.04E-05	0.00E + 00	9.93E-04	2.47E-06	2.16E-03	0.00E + 00	5.64E-04	0.00E + 00
	11 & above	1.81E-04	1.82E-06	2.49E-04	0.00E + 00	4.20E-05	0.00E + 00	1.69E-03	1.70E-05	2.32E-03	0.00E + 00	3.92E-04	0.00E + 00
Ado-Ekiti	below 10	1.47E-04	2.09E-06	1.19E-04	0.00E + 00	4.01E-05	0.00E + 00	1.37E-03	1.95E-05	1.11E-03	0.00E + 00	3.74E-04	0.00E + 00
	11 & above	1.56E-04	2.37E-06	3.25E-04	0.00E + 00	3.42E-05	0.00E + 00	1.46E-03	2.21E-05	3.03E-03	0.00E + 00	3.19E-04	0.00E + 00
Akure	below 10	1.51E-04	1.83E-06	3.17E-04	0.00E + 00	3.62E-05	0.00E + 00	1.41E-03	1.71E-05	2.96E-03	0.00E + 00	3.38E-04	0.00E + 00
	11 & above	9.96E-05	6.41E-06	3.26E-04	0.00E + 00	4.64E-05	0.00E + 00	9.29E-04	5.98E-05	3.04E-03	0.00E + 00	4.33E-04	0.00E + 00

they are disproportionately exposed to environmental contaminants and generally exhibit more severe health effects than adults (Huremović et al., 2020; Witkowska et al., 2021; Aendo et al., 2022. This is attributed to age-related behaviors, such as hand-to-mouth activities, pica, and playing on or near the ground. In Nigeria, metal toxicity is not distinctively documented and non-stringent mechanism for heavy metal pollution has militated against public health (Alghamdi et al., 2019).

Given that high levels of metals of public health importance among children have been well documented (WHO, 2011; Al Osman et al., 2019; Karakis et al., 2021; Heng et al., 2022; Mbunga et al., 2022), the present study further raises concern over the health dangers of people especially children (ages between 0–6 & above) around the homes in the studied areas. The inclusion of heavy metals in paint production have been documented (Apanpa-Qasim et al., 2016; Apanpa-Qasim and Adeyi, 2017).Therefore, the toxicity from paint ingestion or other routes of exposure remains important especially in homes where children reside (Orisakwe et al., 2007; Wani et al., 2015; Hauptman et al., 2017). All samples examined were above the permissible limits set by US Consumer Product Safety Commission for (90 mg/kg of Pb), 25 mg/kg of As, 100 mg/kg of Cd and 60 mg/kg of Cr as regulated by the EU.

The study revealed that paints chips from residential houses in four states of south-western Nigerian state namely Lagos, Ibadan, Akure and Ado-Ekiti, contain high levels of lead and cadmium, which are toxic metals that can cause serious health and environmental problems. The study used Thermo scientific inductively coupled plasma–optical emission spectrometer to measure the concentrations of these metals, as well as other metals such as chromium, copper, iron, manganese, nickel, and zinc. The study found most of the paint chips samples exceeded the WHO and USEPA limits for lead and cadmium, with some samples having extremely high concentrations of up to 25717.95 mg/kg for lead and 5317 mg/kg for cadmium, over 250 times fold above the 90 mg/kg and 53 times fold above the 100 mg/kg permissible limits of Pb and Cd, respectively. These paints pose a risk of exposure to the residents, especially children and pregnant women, who may ingest or inhale the paint chips or dust. The other metals detected in the samples were within the acceptable ranges, but they may have synergistic or antagonistic effects with lead and cadmium, affecting their toxicity and bioavailability. The study concluded that there is a need for strict regulation and enforcement of the use of lead and cadmium in paints, as well as public awareness and education on the hazards of these metals. The study also recommended further research on the sources, pathways, and health impacts of metal exposure from paints chips in residential houses.

Other alternative pigment options can be formulated in paint production. The use of calcined kaolin which also exhibits properties similar to titanium dioxide can be used as an alternative pigment. Its properties include brightness and opacity with the cost of titanium dioxide which was said to be the alternative substitute to be about six times the cost of calcined kaolin products. Kaolin is essential for improving the brightness of colours in paint, as well as controlling the texture for dispersant and coat ability. Kaolin also improves paint in many other ways such as providing less weight per canister, significantly extending the product life, improving opacity, gloss, colour and viscosity. Calcined kaolin is particularly useful in creating crack resistant paint with high gloss and opacity. Particle size plays a large role in determining qualities opacity, gloss, colour and viscosity in paint. Finer kaolin powder will produce brighter colour, more opacity and vice-versa (American elements, 2015). Calcined kaolin gives excellent optical scatter required in paints. Ti, Mg, Mn, are paint fillers

Funding

Part of this research work was granted by The World Academy of Sciences for the Advancement of Science in Developing Countries (TWAS)-Council of Scientific and Industrial Research (India) (FR number: 3240275040)

Conflict of interest statement: The authors declare that they have no conflict of interest

Availability of data and material (data transparency): Available on request

Code availability: 'Not applicable'

Authors' contributions: Ajoke Fehintola Idayat Akindelecarried out sampling, instrumental analysis and manuscript preparation and review.

Akaninyene Joseph contributed in the recommendations and review process to the manuscript

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No competing interests reported.

Lead, Cadmium and other metals in Residential Paint Chips from Indoor wall surfaces

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Abstract

Introduction

Materials and methods