Silver waste distribution in effluents and Gajahwong and Mantras Pioro River segments from the silver craft industry in Kotagede, Yogyakarta, Indonesia

Silver is a hazardous heavy metal that can be found in waters due to effluents from silver crafting. This research aimed to determine the silver contents of effluents from the silver craft industry in Kotagede, Yogyakarta, and analyze the distribution of silver in the receiving bodies of water: Gajahwong and Mantras Pioro River segments. Laboratory tests were conducted to calculate the presence of silver in effluents, river water, and river sediments, and a correlation analysis was employed to investigate the spatial correlation between silver concentrations and silver craft industries. Laboratory test results found silver at <0.0024-88.48 mg/L in effluents. When disposed of into the river, the silver-containing effluents cause contamination in both river segments, as evidenced by <0.0024 mg/L of silver in the water and 2.80-4.04 mg/Kg in the sediment. The distribution pattern also suggested that the concentration of silver increases as the number of silver craft industries on each side of the two river segments increases. In conclusion, the distribution of silver craft industries influences the spread of silver content in the Gajahwong and Mantras Pioro segments.


Introduction
Silver is a hazardous heavy metal.Primary anthropogenic sources of silver in the environment are electroplating and industrial activities that leave metal flakes as the by-products [1].Industrial silver waste is not easily degraded and can be deposited at the bottom of sediment in waters.This is possible because silver nanoparticles bind to organic and inorganic ligands [2] and have low solubility [3].Due to these various hazardous properties, disposing of the silver waste directly into water or the soil can affect environmental quality.
Kotagede in Yogyakarta is one of the centers for silver craft production in Indonesia.However, it has been reported that silver waste from this industry is discharged directly into the environment by draining it into infiltration wells and channels that lead to the river [4].A river is an open body of 1313 (2024) 012006 IOP Publishing doi:10.1088/1755-1315/1313/1/012006 2 water that is vulnerable to various pollutant inputs generated by human activities [5].The silver craft industry in Kotagede is traversed by parts of the Gajahwong and Mantras Pioro Rivers.
Direct disposal of waste into the environment without prior pre-treatment can harm the environmental quality, especially that of aquatic ecosystems.The amount of contaminants released into waters may vary from the upper to the lower reach [1,6,7,8,9], which is contingent on the intensity of human activities in the surroundings.Previous research found that rivers around the silver craft industry have good to very good assimilative capacity to absorb pollutant loads [6].This research, however, does not include silver as a contaminant variable.Meanwhile, the silver content of groundwater in the silver craft industry area in Kotagede has exceeded its maximum allowable concentration, which can seep into and contaminate the river [4].Nevertheless, the presence of silver as a pollutant in the environment is still underresearched, particularly the distribution of silver waste along the receiving rivers.
For the above reasons, this research specifically identifies the concentration of silver in effluents from the silver craft industry in Kotagede and its distribution in the water and sediment in parts of the Gajahwong and Mantras Pioro Rivers.It is focused on mapping active silver craft industries in Kotagede, identifying the effluent channels, and determining silver levels in effluents, river water, and sediments.Further, this research is expected to provide information on whether the spatial distribution of the silver craft industry affects the presence of silver in both river segments.

Study Area
This research was focused on the silver craft industry area and the rivers flowing through it.The selected silver craft industries were those still operating in Kotagede, one of the districts in Yogyakarta City, Indonesia.Kotagede is 307 ha, which is mainly used for residential purposes, including trade, service, and industrial activities (Figure 1).

Data Acquisition
Sampling locations were determined with the purposive sampling technique (see Figure 2).The first set of samples was comprised of three silver craft industries, selected based on differences in product volume per month.The selection of those three industrial samples was carried out by surveying the handicraft production in industries that are still operating and exhibit differences in production volume ranging from low to high (see Table 1).Effluent samples are carried out by collecting the wastewater stored in the waste containers of each craftsman.Therefore, this study does not measure the discharge 4 flow rate of the waste.The effluent samples were collected from these sites and further tested in the laboratory to assess the presence of silver in wastewater released directly into nearby rivers.The second set of samples were those of river water and sediment collected at 7 points along the river segments, which also included on-site measurement of flow discharge as an influencing factor in water quality.Discharge was determined by measuring the width, depth, and flow velocity of a selected river channel using the velocity-area method and a current meter.To convert these measurement results into a discharge value (Q), several steps were followed.First, to obtain flow velocity (v), the number of rotations of the current meter's propeller was counted and inputted into Equation ( 1) together with tool coefficients (a, b).Second, the width of the river channel at a sampling point was spaced vertically to obtain several cross-sectional segments (n) with the width b, and then the cross-sectional area of the flow (A) was calculated using Equation (2).Third, the flow rate or discharge of each cross-sectional segment (Q) was computed by multiplying flow velocity (v) with the cross-sectional area (A), as expressed in Equation ( 3).
The locations of the water and sediment sampling were decided purposively to represent the conditions upstream, within, and downstream of the silver craft industry area (see Figure 2).This selection aimed to provide a comparison to identify contamination by silver waste along the two river segments.Each water and sediment sample was a composite of three samples: two on the edges and one in the middle of the channel.
Silver concentrations in the river segments were analyzed spatially by comparing the test results of the water and sediment samples at each point.Natural factors and human activities contributing to the spatial pattern of silver concentrations were also analyzed.This includes analyzing the effect of locations of silver craft industries on silver distribution by determining silver concentrations in effluents and measuring river flow discharge that controls sedimentation.

Distribution of Silver Craft Industries
The industrial sector is one of the economic activities that have been growing as a major contributor to Indonesia's economy [10].BPS-Statistics Indonesia stated that the country's metal industry developed considerably from 2015 to 2020.Among the numerous products of the metal industry is the silver crafts created in Kotagede District, Yogyakarta.Silver craft industries were not distributed evenly in the region but concentrated in three subdistricts (Purbayan, Prenggan, and Rejowinangun), creating the density shown in Figure 3. Purbayan had the highest industrial site density, while Rejowinangun had the lowest.This uneven distribution can be attributed to the most favorable locations for the industry, which allow for cost-efficient productions due to connection to other businesses in the same sector that supply the input or sell the output of silver crafting [11].This is evidenced by the proximity of silver craft industries to Kotagede Market, which sells silver crafts in Purbayan.

Silver Concentrations in Industrial Effluents
Silver waste is the by-product or residue of various anthropogenic activities (e.g., industry and mining) and can be naturally leached from the soil into waters [12].Silver waste in Kotagede is mainly generated by silver crafting that has long existed in the area, particularly from electroplating and engraving processes that produce silver flakes [1].Here, silver crafting includes applying a certain amount of silver to sculptures before immersing them in an H2SO4 or HNO3 solution in the refining stage.This acid solution can dissolve silver, creating liquid waste.The silver waste that has been formed will be collected by the craftsmen into a large container.The waste will be gathered first before eventually being sold to silver waste collectors or disposed of into water channels leading to rivers and absorption wells around the craft area.Therefore, in this study, the measurement of the waste discharge is not conducted due to the research duration not reaching the waste disposal phase yet.
Figure 4 shows the amount of silver in effluents from Kotagede.It ranged from <0.0024 to 88.48 mg/L, with the smallest concentration found at Industry 1 and the largest at Industry 3.The high presence of silver can be caused by the lack of waste treatment that can reduce 80-90% of the silver content in effluents prior to disposal [13].Moreover, it can be attributed to the scale of the industry [14], as shown in Table 1.Results also showed that the liquid waste produced by silver crafting was drained into infiltration wells, collected in tanks, and flown in a drainage channel into the river.This potentially increases the presence of silver in surrounding waters.

Silver Concentrations in River
Water.Results showed that silver craft industries in Kotagede disposed of their waste directly into the environment by draining it into infiltration wells or channels leading to Gajahwong and Mantras Pioro River segments.Silver was detected at <0.0024 mg/L and evenly distributed along both segments.This figure corresponds to previous research findings, which identified silver at 0.0001 mg/L in river water [17].Low silver contents in a body of water can be attributed to, among others, increasing flow discharge, water sampling time, and waste treatment by the silver craft industry.In the water, silver is likely to bind to other compounds and be deposited in aquatic sediments [18].This corresponds to the characteristics of river sediments that generally absorb metals in waters through a series of physical and chemical processes [19,20].In other words, metals can be found in both river water and sediments.As seen in Figure 6, the sediments in the two river segments that passed through the silver craft industry in Kotagede carried different concentrations of silver.The pattern shows that the concentration increases as the rivers flow downstream.Silver spreads unevenly along the river because its upper, middle, and lower reaches have varying hydrological characteristics that determine sediment movement [18].Kotagede is an urban area characterized by low-flow discharge [21] and perennial flow [22].Moreover, it is located in the middle of a watershed with high levels of pollution [23].These conditions promote sediment transport and deposition in the Gajahwong and Mantras Pioro River segments.

Spatial Correlation between Silver Craft Industries and Silver Concentrations along the River Segments
Numerous anthropogenic activities have been reported as the leading cause of the decline in river water quality [24].An example is industrial activities that release heavy metal pollutants into the environment [25].Figure 7 shows an increase in silver concentration in the two river segments after passing through the silver craft industry in Kotagede, indicating the latter's effect on the former.Places with a high density of silver craft industries (see the red area in Figure 7) were close to river segments with high silver contents.The influence of industrial density on the silver content in the river can be identified using Pearson correlation calculations.The correlation is performed using SPSS software, which compares the density data of silver crafting with the silver content in the river.The density data of silver crafting is obtained by comparing the number of craft activities in a village with the village's area, while the data on silver content in the river represents the accumulation of silver content in the water and sediment of the river.Statistical analysis showed a very strong correlation between the two (0.92), proving that an increase in the number of industrial sites in an area increases the amount of waste produced [26] and released to the environment, thus introducing more pollutants into the river.Figure 7 also illustrates the spatial distribution of the formed silver content within the river.This distribution indicates that the silver content in the Gajahwong River Segment and the Sub-Watershed Segment of Gajahwong experiences an increase in value from upstream to downstream.This phenomenon is due to the volume of industrial activities in the vicinity that affects the amount of waste discharged into the river [26], wherein there is an increase in the volume of silver crafting from low to high in the upstream to downstream areas of the two river segments.In this research, it's noted that the larger the volume of a craft, the greater the amount of waste produced, which consequently affects the silver content in the flow of the surrounding river segment.Furthermore, the increase in silver content from upstream to downstream of the river segment also occurs due to the accumulation of silver content in the downstream area originating from various inflows [27].The inflows received by the river segment in the research area become more varied as they move downstream.The increase in the variation of input flows is shown by the convergence of the main river with tributaries, as well as input flows stemming from various activities around the river segment, as indicated by drainage paths.These diverse inflows carry pollutants that subsequently accumulate in the downstream part of the river segment.

Conclusion
Silver has been found in effluents from the silver craft industry in Kotagede.When disposed of directly into the environment, effluents diminish the water quality of the Gajahwong and Mantras Pioro River segments that traverse the area.As evidence, the concentration of silver in both segments increases after passing through the silver craft industries.Statistically, the presence of silver in river water and sediments strongly correlates with the density or concentration of silver craft industries (0.92).In other words, an increase in the number of industrial sites in an area (i.e., density) affects the amount of silver found in nearby rivers.

Figure 1 .
Figure 1.Land use map of the silver craft industry area in Kotagede

Figure 2
shows the study area and sampling points on both segments.

Figure 2 .
Figure 2. Map of silver craft industries in Kotagede and the sampling points on Gajahwong and Mantras Pioro River segments 3. Methods

Figure 3 .
Figure 3. Map of the site density of silver craft industries in Kotagede, presented by sub-district Source: Data analysis, 2023

Figure 4 .
Figure 4. Concentrations of silver in effluents from silver craft industries in Kotagede (Source: Data analysis, 2023)

Figure 5 .Figure 6 .
Figure 5. Distribution of flow discharge in Gajahwong and Mantras Pioro River segments

Figure 7 .
Figure 7. Distribution of silver waste in Gajahwong and Mantras Pioro River segments based on the density or concentration of silver craft industries in Kotagede (Source: Data analysis, 2023)

Table 1 .
Monthly silver craft productions of the sampled industries in Kotagede

Sampled Silver Craft Industry Location (Sub-district) Weight of Product per Month Categories
[16]ges in the weather can regulate river flows and affect their pollutant contents[15].Figure5shows the distribution of flow discharges in Gajahwong and Mantras Pioro River segments around the silver craft industry in Kotagede.Discharge measurements were conducted during the rainy season in March.Results showed a flow discharge in the range of 0.93 to 5.53 m3/s.The Mentras Pioro River segment had the lowest discharge because it has a smaller catchment area than the Gajahwong River segment.The highest discharge was identified at the confluence of the two river segments.Several factors that determine river flow discharge are the characteristics of the watershed or catchment, including area and rainfall dynamics[16].