## 2 Materials and Method
### Data Collection Procedure  
The 39 clay soil samples (see Figure 1 above) were collected from participants attending antenatal care services and family planning in the four settings in Tshwane District in Gauteng Province. Simple random sampling was followed to include all soil samples collected from participants in the study. The soil samples were first collected and stored in sealed plastic bags for packaging, and then stored in storage bags from the data collection sites. The samples were taken for crushing in preparation for laboratory analysis. The samples were crushed into powder, then poured into 50 mL granular bio tubes.  
The ICP Mass Spectrometer instrument (refer to Figure 2) was used to measure the quantity and detect the chemical content of the clay soil samples collected from the participants in the study. The chemical composition tests were performed by a qualified laboratory and instrument technician at the University of Johannesburg, Gauteng Province, whereby the step-by-step procedures stipulated by the ICP Mass Spectrometer manufacturer were followed to ensure the accuracy of the results. The analysed data for the clay soil samples gave good recoveries, which confirmed the accuracy of the results. The digestion process took place in 2023, followed by the analysis, and the extraction of data.  
Figure 1: Clay soil samples.  
A Metter ToledoXP205 (Mettler Toledo, Columbus, OH, USA) analytic balance (refer to Figure 3) was used to weigh approximately 0.2 g samples to the nearest 1 mg. The samples were transferred to microwave vessels along with 9 mL Suprapure HNO\({}_{3}\) (Merck, Germany) and 3 mL HCl (Merck, Darmstadt, Germany). The samples were centrifuged for 10 min at 6000 rpm. A quick visual inspection was conducted to ensure there are no solid matter suspended during the transfer of samples using pipette. The samples were digested according to a modified method based on United State EPA 3051 protocol. The samples were then heated from a room temperature to 200 \({}^{\circ}\)C for 15 min and kept at 200 \({}^{\circ}\)C for another 10 min. After digestion, the samples were quantitatively transferred and diluted to the 50 mL mark. The samples were diluted an additional 20 times by pipetting 500 micro litres and diluting 10 mL with 1% nitric acid to matrix match with calibration standards. Calibration standards that ranged from 0.1 to 10 \(\upmu\)g/L were prepared from NIST traceable RMs and diluted with 1% nitric acid as well. The ICP Mass Spectrometer was warmed up for a minimum of 30 min to ensure instrument stability and robustness during the analysis. The instrument was tuned according to the specification to acquire the required sensitivity and low oxides. Calibration curves with R\({}^{2}\) > 0.9950 are considered sufficiently linear and indicate that the instrument is performing well. The clay soil samples were then analysed. All elements were measured in the Kinetic Energy Discrimination (KED) mode. AMIS0373 was analysed as a quality control. The laboratory results for the chemical analysis of the clay soil composition were captured using an Ms Excel spreadsheet. The test results confirmed the presence of chemical parameters found in the clay soil collected from the participants, who were women of childbearing age attending antenatal care services and family planning in the healthcare facilities of Tshwane District, Gauteng Province. The chemical elements found in the clay soil samples were detected in different quantities. The results derived from the biochemistry laboratory tests were used to inform the development of a health education and promotion intervention program.  
Figure 2: NexION 300X ICP-MS instrument.