Social Sustainability of Raw Rubber Production: A Supply Chain Analysis under Sri Lankan Scenario

: Raw rubber production is the sole foundation for the rubber product industry, rendering raw rubber to manufacture essential commodities to mankind, such as tires, condoms, surgical gloves, and so forth. Raw rubber production involves various stakeholders; however, literature focusing on the social impacts of the supply chains of raw rubber production has hereto been absent. Social life cycle assessment, a popular tool to assess the social impacts of a product or process and was deployed herein to assess the social proﬁles of three Sri Lankan raw rubber supply chains (crepe rubber, concentrated latex, and ribbed smoked sheets) in a cradle-to-gate manner. The Social Hotspots Database v4 on Sima Pro v9.3 was used for the analysis. Results indicated that Governance, Labour rights & decent work had been affected due to Corruption and Freedom of association & collective bargaining issues, mainly in Belarus and China. Proposed improvement options to address these touchpoints were found to be effective. If the importation of K-fertilizer shifted into countries with lower risks, such as Canada, Israel, and Lithuania, overall social risks associated with Corruption and Freedom of association & collective bargaining could be reduced by ca. 36% and 25%, respectively. As a result, social risks in the impact described above categories, i.e., Governance and Labor rights & decent work, were reduced by ca. 35–41% and ca. 17–20%, respectively. Managers may pay thorough attention to the hotspots identiﬁed herein in the ﬁrst place and try to avoid them as much as possible. They may consider importation from the aforesaid low-risk countries while weighing the trade-offs with economic and environmental aspects.


Introduction
The natural rubber industry is essential in human life, providing indispensable items such as tires, condoms, infant pacifiers, surgical gloves, and many more [1,2].Natural rubber is derived from the sap of rubber trees (Hevea brasiliensis), grown in tropical regions such as Asia, Africa, and South America [3,4].The industry significantly impacts global economic growth and employs millions of people in developing countries [2,5,6].The global natural rubber market is estimated to be worth ca.USD 30 billion in 2022, with Asia holding the largest share of ca.92% [7].
Raw rubber production is the sole foundation for the natural rubber industry, providing raw rubber to manufacture numerous commodities, as mentioned in the preceding paragraph [8].The bark of the rubber tree is tapped to obtain latex which is then processed into different raw rubber products, including crepe rubber, concentrated latex, and ribbed smoked sheets (RSS) [9].Crepe rubber is produced by coagulating rubber latex from a rubber tree, dried, and rolled into thin sheets.Crepe rubber is often used in pharmaceutical items, footwear, and industrial applications such as belts, hoses, and gaskets [5].Concentrated latex is a type of rubber processed through centrifugation, which further separates the rubber particles from the liquid.Centrifuged latex is often used in products that follow the dipping process, such as surgical gloves and condoms [1,10].Ribbed smoked sheets rubber is a rubber sheeting manufactured with low-cost machinery at the lowest cost, but this gives high quality if processed properly [11,12].This rubber is commonly used in tires, rubber bands, and mechanical items [11,13].
In raw rubber production, significant amounts of electrical and heat energy, chemicals, fresh water, and labor are involved [2,3,13].Also, having many factory employees from the local community, there is a close association between the local community and raw rubber manufacturers [14].
With the said nature, the raw rubber sector has faced various economic, environmental, and social challenges.Economic issues include material use inefficiency, poor worker productivity, and higher production expenses [15][16][17].Raw rubber production releases toxic chemicals into the environment, especially through wastewater [18].These chemicals can harm people and wildlife [19,20].Further, it generates large amounts of greenhouse gases, including carbon dioxide and methane, due to the heavy use of electricity and firewood [1,5,11,21,22].In addition, the social impact of the natural rubber industry is also significant.The workers in the industry are typically poor and vulnerable to exploitation.They are often paid low wages and other facilities.Also, pollution-triggered community struggles have been reported [17].
Several studies have tried to address the above economic and environmental issues [4,10,23].Earlier, we endeavored to enhance the environmental and economic sustainability of the production of crepe rubber [5,24], concentrated latex [1], and RSS [11].However, literature focusing on the social impacts or issues of raw rubber production has been limited.
Social life cycle assessment (SLCA) is a tool commonly used in scientific research to assess the overall social impacts of products.Despite its widespread use, methodology development in SLCA is still progressing [25].This systematic approach can assist companies in administering their supply chains and promoting social responsibility and sustainability by evaluating products' social and socioeconomic aspects throughout their life cycle [26,27].Hence, it has been applied to different product value chains for social hotspots and improvements, using SLCA databases as a data source (see Table 1).
We also attempted to analyze the social impacts of a crepe rubber processing estate in Sri Lanka using a novel social life cycle assessment framework [14], being a site-specific analysis that had no capability of capturing the social hotspots along the supply chain.This conveys that studies analyzing the social sustainability of the entire raw rubber production supply chain are absent.As mentioned in the preceding paragraph, such an attempt is crucial in establishing the overall social sustainability of the natural rubber industry.To address this gap, we conduct SLCA focusing on three main raw rubber supply chains in Sri Lanka (crepe rubber, concentrated latex, and RSS), a country that ranks as the 13th largest rubber producer in the world and renowned as the largest exporter of best high-quality crepe rubber to the global market [14,28,29].Crepe rubber, concentrated latex, and RSS comprise a share of ca.90% of inland raw rubber production [30].

Rubber Cultivation
The rubber plantation cycle considered herein spans over 25 years and is comprised of the nursery (one year), immature (five to seven years), and mature (over 18 years) stages [42,43].During the nursery stage, seeds are collected from mature rubber trees and put in a nursery.At the early stage of growth, plants are bud grafted with scions of required genotypes.After the plants are mature enough to survive independently, they are transplanted into a field.Before planting rubber plants in the field, the land is cleared and prepared by removing obstructions and weeds.The soil is then tilled and fertilized to make it suitable for the growth of rubber trees [44].
Rubber trees typically require at least five years to enter the mature phase, where the rubber trees are ready for harvest.During the immature phase, the transplanted rubber plants are cared for to ensure healthy growth and development.Pruning may be necessary to ensure the tree's proper shape and size.Rubber trees are susceptible to some pests and diseases.Application of insecticides or fungicides may be required to protect the tree from these threats [44].
Optimal growth and yields can be attained only by properly balancing the nutrients per need of the rubber plant.Most rubber-growing soils in Sri Lanka are deficient in nitrogen (N), phosphorus (P), potassium (K), and magnesium (Mg).However, these deficiencies could easily be remedied by applying inorganic fertilizers in the proper proportions and amounts.The most common fertilizers used are urea (for N), rock phosphate (for P), muriate of potash (MOP; for K), kieserite (KIE; for Mg), and dolomite (for Mg).These fertilizers are typically applied to the soil around the base of the tree [45].

Crepe Rubber Manufacture
First, rubber is tapped from the rubber tree and transported to the crepe rubber processing factory using bowsers.Before transporting, sodium sulfite is added as a preservative to the rubber to control fungal growth.At the factory, fresh latex is standardized, where its yellow pigments are fractionated, leaving the white fraction, which contains the majority of rubber particles in liquid form.Here, as per dry rubber content (DRC), sodium bisulfite and water are added.Yellow fraction comprises only ca.10% of DRC [3].The white fraction is then transferred to different containers while mixing with water, formic acid, and bleaching agents in the coagulating process.Then, the coagulum of the white fraction is cut into cube-like pieces and passed through a set of roller mills, a macerator, a diamond roller, and a smooth roller.The primary purpose of milling is to reduce the size of bulky coagulum pieces (with high water content) by pressing them into thin laces of rubber (containing less water).Thin laces are then draped over a drying tower and left for three to four days.Dried crepe laces are stacked, folded into 25 kg mats, and passed through a roller mill called a dry blanket mill, resulting in soft-edged rubber blankets.After the rubber blankets are cut to the customer's desired size, they become known as blanket crepe rubber.The final step in the production of crepe rubber is the visual grading and packaging of the product for sale.The yellow fraction is further processed following the same procedure to obtain a lower-grade crepe rubber.

Concentrated Latex Manufacture
In latex collection and transportation to the factory, ammonia is added as a preservative to avert fungal growth in field latex.Upon arrival at the factory, a laboratory test measures the latex's DRC and ammonia concentration.Then the latex is sifted through a 60-mesh sieve and collected in bulking tanks.The bulking tanks are filled with a mixture of tetramethyl thiuram disulfide (TMTD) and zinc oxide (ZnO) (often referred to as T.Z.), diammonium hydrogen phosphate (DAHP), and lauric soap.DAHP functions as a magnesium ion (Mg 2+ ) remover, whereas others act as preservatives.Mg 2+ elimination is crucial because the presence of Mg 2+ encourages bacterial growth [3].Decantation is performed to remove Mg 2+ in the form of magnesium ammonium phosphate.The remaining field latex is then centrifuged in centrifuge separators.Field latex is separated into two segments at the separators: concentrated latex and skim latex, with %DRCs of ca.60% and 3-6%, respectively.Acquired concentrated latex is preserved in steel tanks, with the ammonia concentration kept per customer specifications, i.e., high Ammonia (about 0.7%) or low Ammonia (about 0.2%), until dispatch.Skim latex is coagulated with sulfuric acid in a separate tank (the coagulation tank).After that, the coagulum is removed and pressed to get skim rubber laces.The laces are then air-dried before being mechanically pressed into rubber sheets (dry blanket milling).After that, the blankets are cut into tile-shaped segments and packaged as a skim crepe.

Ribbed Smoked Sheets Manufacture
Smallholders with less than five acres of rubber plantations manufacture RSS in Sri Lanka.RSS facility at this caliber can process up to 40 kg of rubber daily [3].First, rubber trees are tapped to get fresh latex and handled at the mills.When latex arrives at the factory, it is coagulated by passing through a series of flat pans with water and formic acid.Then, the coagulum is milled using two hand-operated rollers, termed smooth and grooved rollers.The coagulum is passed through the smooth roller two to three times before being passed through the grooved roller once.Milled sheets are cleaned and placed in a shade for dripping before being smoke-dried.Smoke-drying involves hanging sheets in a smokehouse for three to five days.Finally, the dried sheets are weighed and transported to regional retail centers.

Social Life Cycle Assessment
SLCA is a systematic approach to assess the social impacts of a product or system throughout its life cycle, from material extraction to final disposal or recycling [46].SLCA is a relatively new tool for which a standardized methodology is yet to be proposed [47].However, SLCA follows ISO14040/44 [48,49], the international standard for LCA.The first comprehensive framework for SLCA was published in 2009 [50], termed UNEP/SETAC Guidelines for Social Life Cycle Assessment of Products.Therein, five stakeholder categories (Workers, Local community, Society, Value chain actors, and Consumers) have been specified with six impact categories (i.e., Human rights, working conditions, Health & Safety, Development of the country, Socio-economic repercussion, and Governance) for developing social life cycle inventories [51].To facilitate this process, a set of subcategories (e.g., Forced labor, Discrimination, etc.) were also defined at each stakeholder category and were set to assess using inventory indicators.A few years later, UNEP/SETAC Methodological Sheets for the Subcategories of SLCA were published to provide practical guidance for conducting SLCA case studies [52].This document supplemented the above subcategories with inventory indicators and potential data sources.Various entities have developed SLCA databases and frameworks based on the above documents.For instance, NewEarth B released Social Hotspots Database [53] in 2013 to assess the social risks of product supply chains.A group of six companies with PRé Sustainability devised the framework of Product Social Impact Assessment in 2014 [54] to render practical guidance to performing SLCA of products at the corporate level; this framework has been updated at several stages ever since.The latest version of the UNEP/SETAC SLCA code of practice was released in 2020 (i.e., Guidelines for social life cycle assessment of Products and Organizations 2020) [49].It provided extra guidance for the steps of SLCA from the lessons learned from the previous version.It touched on different areas of evaluating social issues of organizations and products, e.g., linking SLCA with the Sustainable Development Goals of the United Nations and Social Organizational life cycle assessment.
Figure 1 depicts an overview of the SLCA framework followed herein.Rectangles, Rectangles with rounded corners, and ovals represent the processes, inputs to specific processes, and outputs from processes, respectively.Sections 3.2-3.7 provide detailed descriptions of this framework.

Goal and Scope Definition
We aim to analyze the social footprint of the three raw rubber supply chains, i.e., crepe rubber, concentrated latex, and RSS, seek avenues for improvements, and foresee their potential degrees of improvement when the upgrades are in place.The system boundary of the study is demarcated in Figure 2, in which the foreground system encapsulates the processes directly involved with raw rubber production on a cradle-to-gate basis (i.e., from rubber cultivation to manufacture).Such processes require site-specific data [55].Meanwhile, items that are linked with background supply chains are indicated by shaded boxes, where sector-or country-level data (or generic data) are necessary (see inventory analysis section for more details on data collection) [55].The functional unit for the study was set as delivering 1 tonne of product, i.e., white crepe, concentrated latex, and RSS.We follow the basic steps of ISO 14040/44 for the study [48,49].

Goal and Scope Definition
We aim to analyze the social footprint of the three raw rubber supply ch crepe rubber, concentrated latex, and RSS, seek avenues for improvements, and their potential degrees of improvement when the upgrades are in place.The boundary of the study is demarcated in Figure 2, in which the foreground system sulates the processes directly involved with raw rubber production on a cradl basis (i.e., from rubber cultivation to manufacture).Such processes require site data [55].Meanwhile, items that are linked with background supply chains are i

Life Cycle Inventory Analysis
The second step involves collecting inventory data for background and foreground processes, which will later be used to model and evaluate potential social impacts at the impact assessment stage [56].Initially, at this step, the system(s) being examined must be modeled using both site-specific (or foreground) data and generic data (or background data related to the supply chain).Foreground data refer to the data collected specifically for the analysed system [55].Background data refer to the data used as inputs for the assessment that are not specific to the product being evaluated [56].Accordingly, data were collected on the amounts of materials and energy inputs at the different stages of the life cycle within the system boundary, the economic sectors that those inputs belong to regions where the materials and energy are sourced from, and the unit price of material and energy [56].
Background information can be found in SLCA databases, and Social Hotspot Data base (SHDB) was used in this regard [53].SHDB provides three types of information; (1 supply chain composition, (2) labor intensity; and (3) social risks [56].Provision No. 1 and 2 uses the Global Trade Analysis Project (GTAP) global economic equilibrium model ver sion 9 [57].Regarding No. 1, SHDB holds the trade flows between 57 economic sector from 140 countries in 2011.Along with foreground data, the SHDB can compute trade flows of related sectors or regions.As for No. 2, SHDB determines the labor intensity by the "working hours per U.S. dollar of product output" for the year 2011 for each of the 57 economic sectors in each of the 140 countries, calculated by dividing GTAP data of tota wage payments (U.S. dollars) per U.S. dollar of output by the sector/region average wage (U.S. dollars/hour) [58].Regarding No. 3, SHDB holds the social risks information of ove 160 social inventory indicators for 140 regions and 57 sectors and uses various sources fo obtaining them (e.g., intergovernmental databases (e.g., ILO database), country statistics literature, etc.).Risk information, for instance, the indicator: "percentage of the population living under USD 2 per day", is used to attribute risk for the social subcategory: "Poverty" under the "Labor Rights and Decent Work" impact category (see impact assessment sec tion for more details) [58].
Foreground data for the study was collected from different sources, as given below Activity data on fertilizer use and unit prices in Sri Lanka were obtained from the Soils &

Life Cycle Inventory Analysis
The second step involves collecting inventory data for background and foreground processes, which will later be used to model and evaluate potential social impacts at the impact assessment stage [56].Initially, at this step, the system(s) being examined must be modeled using both site-specific (or foreground) data and generic data (or background data related to the supply chain).Foreground data refer to the data collected specifically for the analysed system [55].Background data refer to the data used as inputs for the assessment that are not specific to the product being evaluated [56].Accordingly, data were collected on the amounts of materials and energy inputs at the different stages of the life cycle within the system boundary, the economic sectors that those inputs belong to, regions where the materials and energy are sourced from, and the unit price of materials and energy [56].
Background information can be found in SLCA databases, and Social Hotspot Database (SHDB) was used in this regard [53].SHDB provides three types of information; (1) supply chain composition, (2) labor intensity; and (3) social risks [56].Provision No. 1 and 2 uses the Global Trade Analysis Project (GTAP) global economic equilibrium model version 9 [57].Regarding No. 1, SHDB holds the trade flows between 57 economic sectors from 140 countries in 2011.Along with foreground data, the SHDB can compute trade flows of related sectors or regions.As for No. 2, SHDB determines the labor intensity by the "working hours per U.S. dollar of product output" for the year 2011 for each of the 57 economic sectors in each of the 140 countries, calculated by dividing GTAP data of total wage payments (U.S. dollars) per U.S. dollar of output by the sector/region average wage (U.S. dollars/hour) [58].Regarding No. 3, SHDB holds the social risks information of over 160 social inventory indicators for 140 regions and 57 sectors and uses various sources for obtaining them (e.g., intergovernmental databases (e.g., ILO database), country statistics, literature, etc.).Risk information, for instance, the indicator: "percentage of the population living under USD 2 per day", is used to attribute risk for the social subcategory: "Poverty" under the "Labor Rights and Decent Work" impact category (see impact assessment section for more details) [58].
Foreground data for the study was collected from different sources, as given below.Activity data on fertilizer use and unit prices in Sri Lanka were obtained from the Soils & Plant Nutrition Department of the Rubber Research Institute of Sri Lanka (RRISL).They were based on an annual mean over the plantation cycle of 25 years and productivity (on a dry basis) of 1 tonne/ha/year.Data on fungicides, herbicides, insecticide use, and diesel used for tillage were unavailable specifically for Sri Lanka.However, they could be considered common to any rubber-growing country.Therefore, those were gathered from literature (i.e., [42,43]) with prices from IndiaMART [59].Material and energy inputs related to rubber manufacture were gathered from our previous research on crepe rubber [5,24], concentrated latex [1], and RSS manufacture [11].Low-ammonia concentrated latex manufacturing was considered common in the Sri Lankan context [1].
Unit prices for material and energy inputs in rubber manufacture were taken from our recent publications [1,5,11,24].Firewood and water required to manufacture crepe rubber and RSS are usually obtained within the estates.Hence no purchase cost has been considered.To be compatible with the GTAP model of SHDB, USD values gathered were standardized to match USD 2011 values using an online inflation calculator [60] (N.B.This tool is based on the consumer price index, which is a commonly used measure of inflation that tracks changes in the prices of goods and services over time).The regions from which the materials and energy were sourced were identified through RRISL, the Observatory of Economic Complexity (OEC) [61] and Volza databases [62].The economic sectors corresponding to the inputs were determined using the GTAP manual [57].Please refer to the Supplementary Material for more details on foreground data.
By integrating foreground data with background data from SHDB version 4 [53], we mapped three rubber supply chain models on SimaPro version 9.3 software [63].

Life Cycle Impact Assessment
This stage involved transforming inventory data collected in the preceding step into potential social impacts.The impact assessment phase in SHDB included 26 subcategories (e.g., Child labor, forced labor, etc.) aggregated into five impact categories, i.e., Labor rights & decent work, Human rights, Health & Safety, Governance, and Community.Around 160 social impact indicators were used to evaluate these subcategories, with some evaluated with a single indicator and others evaluated with multiple indicators [58].Each indicator has four defined risk levels (very high, high, medium, and low) with a corresponding characterization factor (10, 5, 1, and 0.1, respectively) that reflects the relative probability of an adverse situation happening [58].With the given value '1', the medium risk level has been the basis for assigning relative probabilities to other levels.With Sima Pro v9.3, SHDB combined these characterization factors with inventory data acquired in the previous step to quantify the potential social impacts in Medium Risk Hours equivalent (Mrheq) [58].Accordingly, the product of working hours and their risk levels provides the value of Mrheq.For instance, if child labor in sector A in country B is potentially at very high risk and the working hours to produce USD 1 of the final product is 1 h, the Mrheq of sector A becomes 10 × 1 = 10.
Ultimately, analyses provided three types of results, i.e., the social footprint, salient risks, and social hotspots.Social footprint refers to the overall impact of purchase supply chains, measured in Mrheq.This index highlights the supply chains that contribute the most to overall risks and the impact categories with the highest Mrheq values.Salient risks are the subcategories that account for a greater share of the overall risk [38].Social hotspots are individual production activities or countries contributing significantly to the overall risk by impact category or subcategory [38].
The aggregation method, "Social hotspot 2019 Subcat & Cat Method w Damages", was deployed to calculate the said indexes within SHDB [38,56].

Improvement Proposals
Firstly, we identified the most critically affected impact categories regarding social footprint results.Here, a contribution level of 20.0% was considered initially to identify the critically affected impact categories.Then, the highest contributing subcategories to those impact categories were identified.Thirdly, hotspot analyses were conducted to identify the sectors contributing significantly to the overall risk by the identified subcategories.
Considering the level of contributions, a minimum level of 10.0% contribution level was kept initially to identify the most influential hotspots.Accordingly, alternative options were proposed to minimize the social risks.

Benefit Validation
Finally, the benefits of the alternative options proposed in the previous step were validated through a scenario analysis, where inventory was adjusted based on the nature of the alternative options before re-executing the impact assessment.

Interpretation
The final step of the framework was to analyze and interpret the outcomes of each stage by being interactive with them.

Results and Discussion
4.1.Social Footprints and Salient Risks in Supply Chains of Three Raw Rubber Types Figure 3 illustrates the social footprints of three raw rubber types in Sri Lanka (in terms of medium risk hours equivalent (Mrheq) per 1 tonne of rubber product) as given by supply chain analyses.The social footprint of rubber cultivation has been higher than that of rubber manufacturing and transportation (which is negligibly handled by the factory of manufacturing) in all three cases.Comparably larger amounts of material use (especially chemicals and fertilizer) during rubber cultivation have been the roots of such results.Due to higher processing intensity, crepe rubber and concentrated latex supply chains showed larger Mrheq than RSS.Most critical social issues have been related to Governance for all supply chains.Further, Labor rights & decent work and Health & safety hold second and third places for all supply chains.'Human rights' has been the least affected.
Considering the level of contributions, a minimum level of 10.0% contribution level was kept initially to identify the most influential hotspots.Accordingly, alternative options were proposed to minimize the social risks.

Benefit Validation
Finally, the benefits of the alternative options proposed in the previous step were validated through a scenario analysis, where inventory was adjusted based on the nature of the alternative options before re-executing the impact assessment.

Interpretation
The final step of the framework was to analyze and interpret the outcomes of each stage by being interactive with them.

Social Footprints and Salient Risks in Supply Chains of Three Raw Rubber Types
Figure 3 illustrates the social footprints of three raw rubber types in Sri Lanka (in terms of medium risk hours equivalent (Mrheq) per 1 tonne of rubber product) as given by supply chain analyses.The social footprint of rubber cultivation has been higher than that of rubber manufacturing and transportation (which is negligibly handled by the factory of manufacturing) in all three cases.Comparably larger amounts of material use (especially chemicals and fertilizer) during rubber cultivation have been the roots of such results.Due to higher processing intensity, crepe rubber and concentrated latex supply chains showed larger Mrheq than RSS.Most critical social issues have been related to Governance for all supply chains.Further, Labor rights & decent work and Health & safety hold second and third places for all supply chains.'Human rights' has been the least affected.Figures 4-6 illustrate the contribution of activities related to crepe rubber, concentrated latex, and RSS supply chains to the social risks in each subcategory.Supply chains associated with the rubber cultivation stage tend to dominate all graphs.For instance, MOP (K-fertilizer) and urea supply chains account for larger proportions of social risks in most subcategories.Notably, the MOP (K-fertilizer) supply chain overshadows the subcategories 'Injuries & fatalities and 'Unemployment', while the urea supply chain does the same for the 'Children out of the school'.However, all graphs recorded the largest contributor to 'Access to drinking water' as the herbicide supply chain.
Further, the DAHP supply chain contributes considerably to the same subcategory in the concentrated latex supply chain.The electricity supply chain shows a considerable contribution to risks at 'Excessive working time' and 'Indigenous rights' regarding the crepe rubber supply chain as the electricity demand remains larger than concentrated latex manufacture.Formic acid, the only purchase supply chain at RSS manufacture, contributes negligibly to all subcategories.

Improvement Proposals
Considering the impact categories having more than 20.0% contribution to the social footprints in Figure 3, we focus on improving the social risks related to Governance, Labor rights & decent work.To do so, subcategories under the respective impact categories were investigated first.
We identified that a larger proportion of social issues related to Governance are from the subcategory Corruption for three rubber supply chains (i.e., crepe rubber: 56%; concentrated latex: 55%; RSS: 54%) (see Figure S1 in Supplementary Material).Similarly, the largest contribution to Labor rights & decent work was from the Freedom of association & collective bargaining (i.e., crepe rubber: 22%; concentrated latex: 21%: RSS ca.22%) (see Figure S2 in the Supplementary Material).
Then, hotspot analyses were conducted to determine the contribution of each country and sector involved in the three production lines under the most influential subcategories identified, i.e., Corruption, and Freedom of association & collective bargaining.
Figures 7-9 illustrate the results of hotspot analyses by supply chain (directly involving sectors with more than 3.0% of contribution to the social risks have been labeled for convenience).The sector named 'Chemical, rubber, plastic products' in Belarus poses the most significant social risk in all three supply chains under the two subcategories of the database, namely, Corruption and Freedom of association & collective bargaining.The sector mentioned above produces K-fertilizer required at the rubber cultivation stage (N.B., ca.52% of K-fertilizer is imported from Belarus; see Table S1 in the Supplementary Material).Due to the importation of urea fertilizer from China (Ca.42% of urea imported from China; see Table S1 in the Supplementary Material), herbicides from India (solely imported from India; see Table S1 in the Supplementary Material), and the social situation in Sri Lanka, the following three significant sectors contributing to social risks are the Chemical, rubber, plastic products in China, then the same in India and the Electricity sector in Sri Lanka, respectively.The Electricity sector in Belarus can be deemed an indirectly involved upstream sector that links with the Chemical, rubber, and plastic products sector in Belarus.

Improvement Proposals
Considering the impact categories having more than 20.0% of contribution to the social footprints in Figure 3, we focus on improving the social risks related to Governance, Labor rights & decent work.To do so, subcategories under the respective impact categories were investigated first.
We identified that a larger proportion of social issues related to Governance are from the subcategory Corruption for three rubber supply chains (i.e., crepe rubber: 56%; concentrated latex: 55%; RSS: 54%) (see Figure S1 in Supplementary Material).Similarly, the largest contribution to Labor rights & decent work was from the Freedom of association & collective bargaining (i.e., crepe rubber: 22%; concentrated latex: 21%: RSS ca.22%) (see Figure S2 in the Supplementary Material).
Then, hotspot analyses were conducted to determine the contribution of each country and sector involved in the three production lines under the most influential subcategories identified, i.e., Corruption, and Freedom of association & collective bargaining.
Figures 7-9 illustrate the results of hotspot analyses by supply chain (directly involving sectors with more than 3.0% of contribution to the social risks have been labeled for convenience).The sector named 'Chemical, rubber, plastic products' in Belarus poses the most significant social risk in all three supply chains under the two subcategories of the database, namely, Corruption and Freedom of association & collective bargaining.The sector mentioned above produces K-fertilizer required at the rubber cultivation stage (N.B., ca.52% of K-fertilizer is imported from Belarus; see Table S1 in the Supplementary Material).Due to the importation of urea fertilizer from China (Ca.42% of urea imported from China; see Table S1 in the Supplementary Material), herbicides from India (solely imported from India; see Table S1 in the Supplementary Material), and the social situation in Sri Lanka, the following three significant sectors contributing to social risks are the Chemical, rubber, plastic products in China, then the same in India and the Electricity sector in Sri Lanka, respectively.The Electricity sector in Belarus can be deemed an indirectly involved upstream sector that links with the Chemical, rubber, and plastic products sector in Belarus.   .Sectors with more than 3.0% contribution are labeled.Red text: x ≥ 10.0%; orange text: 10.0% > x ≥ 5.0%; green text: 5.0% > x ≥ 3.0%.Grey text signifies indirectly involved sectors.Sectors with less than 3.0% contribution are signified by bluish portions.For more details on hotpot sectors, see Tables S9 and S10 in the Supplementary Material.BLR, CHN, LKA, and IND refer to Belarus, China, Sri Lanka, and India.
In the proposal for improvements, hotspot sectors contributing more than 10.0% were considered initially; therefore, the Chemical, rubber, and plastic product sector in Belarus had been the focus.SHDB ranks its inventory indicators for Corruption (i.e., Overall corruption) and Freedom of association & collective bargaining (i.e., Overall risk of freedom of association) in Belarus as Very high.Similarly, 'Very high' or 'High' risk levels have been assigned to the same inventory indicators of the other hotspot sectors (i.e., the Chemical, rubber, and plastic products sector in China and India and the Electricity sector   Sectors with less than 3.0% contribution are signified by bluish portions.For more details on hotpot sectors, see Tables S9 and S10 in the Supplementary Material.BLR, CHN, LKA, and IND refer to Belarus, China, Sri Lanka, and India. In the proposal for improvements, hotspot sectors contributing more than 10.0% were considered initially; therefore, the Chemical, rubber, and plastic product sector in Belarus had been the focus.SHDB ranks its inventory indicators for Corruption (i.e., Overall corruption) and Freedom of association & collective bargaining (i.e., Overall risk of freedom of association) in Belarus as Very high.Similarly, 'Very high' or 'High' risk levels have been assigned to the same inventory indicators of the other hotspot sectors (i.e., the Chemical, rubber, and plastic products sector in China and India and the Electricity sector   In the proposal for improvements, hotspot sectors contributing more than 10.0% were considered initially; therefore, the Chemical, rubber, and plastic product sector in Belarus had been the focus.SHDB ranks its inventory indicators for Corruption (i.e., Overall corruption) and Freedom of association & collective bargaining (i.e., Overall risk of freedom of association) in Belarus as Very high.Similarly, 'Very high' or 'High' risk levels have been assigned to the same inventory indicators of the other hotspot sectors (i.e., the Chemical, rubber, and plastic products sector in China and India and the Electricity sector In the proposal for improvements, hotspot sectors contributing more than 10.0% were considered initially; therefore, the Chemical, rubber, and plastic product sector in Belarus had been the focus.SHDB ranks its inventory indicators for Corruption (i.e., Overall corruption) and Freedom of association & collective bargaining (i.e., Overall risk of freedom of association) in Belarus as Very high.Similarly, 'Very high' or 'High' risk levels have been assigned to the same inventory indicators of the other hotspot sectors (i.e., the Chemical, rubber, and plastic products sector in China and India and the Electricity sector in Sri Lanka) (see Table S11 in the Supplementary Material).However, relatively high K-fertilizer requirements per functional unit, unit price, and labor intensity (i.e., working hours per U.S. dollar of product output) of the sector tend to significantly augment the social risks associated with 'Chemical, rubber, and plastic products sector in Belarus, along with its risk levels assigned to the inventory indicators under Corruption and Freedom of association & collective bargaining (i.e., Overall corruption and Overall risk of freedom of association).
Having 20% of K-fertilizer being imported from Lithuania (a relatively low social risk country where inventory indicators of Corruption and Freedom of association & collective bargaining are at 'Medium' risk levels) at present, there could be a possibility of increasing this amount up to 77% for avoiding the impact associated with Belarus.According to personal communication with officials of the Fertilizer Secretariat of Sri Lanka, the K-fertilizer has recently been imported from Israel, Jordan, Laos, Malaysia, Vietnam and Canada within the price range (in terms of CIF) of USD 850 to 950 per tonne.Therefore, this confirms the possibility of importing K-fertilizer from socially lower-risk countries (Countries where inventory indicators of Corruption and Freedom of association & collective bargaining are at 'Medium' or 'Low' risk levels) such as Canada, Israel, and Lithuania (see Table S11 in the Supplementary Material).We learned that the importation of fertilizer is currently being done considering the commercial value, availability of required amounts at the correct time, the trade balance between the relevant country, physical quality of material, credit facilities provided by the supplier, etc.However, no consideration has been given to social risks in the country of origin, particularly the sectors 'Corruption and Freedom of association & collective bargaining' revealed by the present study.Assuming equal amounts of K-fertilizer are imported from aforesaid countries with lower risks (i.e., Canada, Israel, and Lithuania) to avoid the social risks associated with the importation of the from Belarus, the scenario analysis was implemented.

Benefit Validation
As per scenario analysis, overall social risks associated with Corruption in the supply chains can be reduced by ca.36% if the importation of K-fertilizer shifted into low-risk countries.Similarly, it has impacted Freedom of association & collective bargaining by reducing ca.25% of risks.As a result, social risks in two targeted impact categories, i.e., Governance and Labor rights & decent work, have remarkably been reduced by ca.35-41% and ca.17-20%, respectively (see Figure 10).Also, other impact categories showed notable improvements; for instance, the impact category 'Health & safety' has been improved by ca.22%.However, this has had a relatively low impact on the impact category of 'Human rights'.
This paper highlights the significance of considering the entire supply chain when performing SLCA.Neglecting to do so may result in overlooked impacts in various geographic regions where imports are involved.Moreover, it emphasizes the importance of refining the supply chain by eliminating identified hotspots to enhance the social sustainability of the product being manufactured.This paper highlights the significance of considering the entire supply chain when performing SLCA.Neglecting to do so may result in overlooked impacts in various geographic regions where imports are involved.Moreover, it emphasizes the importance of refining the supply chain by eliminating identified hotspots to enhance the social sustainability of the product being manufactured.
Improvements were identified as promising and can further be magnified by addressing the next levels of hotspots identified herein.More specifically, the Chemical, rubber, and plastic product sector in China and the Electricity sector in Sri Lanka, which involves urea and electricity supply chains, respectively, may be the next touch points.Addressing the former issue may be achievable in the short term.However, resolving the latter may require more time and effort.In this regard, the Sri Lankan government should implement a comprehensive anti-corruption policy that outlines the laws, regulations and punishments for acts of corruption.This policy must be widely disseminated and understood by all stakeholders in the energy sector so that corruption can effectively be deterred.
To improve the conditions of Freedom of association & collective bargaining in the energy sector in Sri Lanka, it is essential to ensure that workers' rights are more respected than present.Moreover, the government should incentivize private companies to enter the energy sector fairly and transparently and comply with relevant labor laws [64,65] Furthermore, the government should collaborate with private companies and trade unions to develop a skills training program for energy sector workers.
Under a situation where previous SLCA studies had overlooked the natural rubber industry, one of our previous studies (site-specific) on a Sri Lankan rubber estate revealed that the production of crepe rubber significantly impacted the workers' social benefits health and safety [14].In contrast, using generic social data, this study unveiled a border Improvements were identified as promising and can further be magnified by addressing the next levels of hotspots identified herein.More specifically, the Chemical, rubber, and plastic product sector in China and the Electricity sector in Sri Lanka, which involves urea and electricity supply chains, respectively, may be the next touch points.Addressing the former issue may be achievable in the short term.However, resolving the latter may require more time and effort.In this regard, the Sri Lankan government should implement a comprehensive anti-corruption policy that outlines the laws, regulations, and punishments for acts of corruption.This policy must be widely disseminated and understood by all stakeholders in the energy sector so that corruption can effectively be deterred.
To improve the conditions of Freedom of association & collective bargaining in the energy sector in Sri Lanka, it is essential to ensure that workers' rights are more respected than present.Moreover, the government should incentivize private companies to enter the energy sector fairly and transparently and comply with relevant labor laws [64,65].Furthermore, the government should collaborate with private companies and trade unions to develop a skills training program for energy sector workers.
Under a situation where previous SLCA studies had overlooked the natural rubber industry, one of our previous studies (site-specific) on a Sri Lankan rubber estate revealed that the production of crepe rubber significantly impacted the workers' social benefits, health and safety [14].In contrast, using generic social data, this study unveiled a border spectrum of social risks concealed behind the far corners of the supply chains of raw rubber.This time also, we found that Health & safety is one of the critically affected impact categories that need to be thoroughly considered after Labor rights & decent work as the improvement continues.However, in our view, combining site-specific and generic analyses would uplift the clarity of these issues, thereby paving the way for the comprehensiveness of decision-making using SLCA.
The Methodology followed by SHDB calculates potential social risks based on characterization factors that reflect the relative probability of an adverse situation happening [58].Therefore, the outcome may not reflect a realistic social profile.If indicators can be evaluated using site-specific data, aforesaid characterization factors could potentially be replaced by performance levels to reflect social performances that can represent a more realistic picture of social profiles.This could be an important area that requires further investigation by future research.
Managers may pay thorough attention to the hotpots identified herein in the first place and try to avoid those hotspots as much as possible and carry out importation from low-risk countries considering the trade-offs with economic and environmental aspects [66].Once the hotspots identified herein are addressed, new ones may emerge.For instance, the possibility for Health & safety to become the most critically affected impact category is higher; hence new hotspots may emerge.Therefore, continuously addressing these issuesfor example, following the Plan, Do, Check, and Act (PDCA) cycle-can significantly reduce social footprints.This type of effort can also help achieve net positive social impacts by creating social handprints [38,58].Outcomes can be publicized in CSR reports and shared with peers to educate and encourage them to do the same.
Further, workshops can be organized in collaboration with LCA experts to educate the responsible personnel in the natural rubber industry on SLCA, as this analysis procedure requires extensive knowledge of SLCA itself.Once sufficient knowledge is acquired, factories can conduct their analyses independently.Till then, managers may have to consult LCA experts.
Since this study was based on generic social data from the SHDB (i.e., supply chain composition, labor intensity, and social risks) and the import ratios and unit prices that are prone to fluctuate, the potential social risks observed herein may differ from those associated with real-world processes for the time being [38].This could be a major limitation of this study.Therefore, the supply chain may be analyzed using site-specific data to appraise social performances rather than potential social risks.Such an analysis could uncover more accurate and insightful information (such as positive and negative social impacts) about the supply chains considered in this study.However, it should be noted that this process may require a significant amount of data and effort.Following the footsteps of this study, natural rubber supply chains based in other countries may be evaluated by future research; such attempts may unveil not only the hotspots but also create avenues for collaborative benchmarking between different natural rubber supply chains to uplift their social performances and thereby to achieve social sustainability.

Conclusions
This paper could successfully unveil the underlying potential social risks of three main raw rubber supply chains, crepe rubber, concentrated latex, and RSS in Sri Lanka.The social footprint of rubber cultivation has been higher than that of rubber manufacturing and transportation due to the heavy material intensity at the cultivation stage.This paper also highlighted the social hotspots and potential degrees of improvement that can be achieved through refining those supply chains.More specifically, Governance Labor rights & decent work have been affected due to Corruption and Freedom of association and collective bargaining, mainly associated with Belarus and China's Chemical, rubber, and plastic products sectors and the Electricity sector in Sri Lanka.Improvements were observed to be promising upon the addressing of those hotspots.For instance, if the importation of K-fertilizer shifted into countries with lower risks, overall social risks associated with Corruption and Freedom of association & collective bargaining in the supply chains could be reduced by ca.36% and 25%, respectively.As a result, social risks in two targeted impact categories, i.e., Governance and Labor rights & decent work, were reduced by ca.35-41% and ca.17-20%, respectively.Therefore, relevant officials like managers may put their hands on urgently addressing these issues by avoiding the identified hotspots.

Figure 1 .
Figure 1.The framework of the study.Rectangles with rounded corners and ovals repr processes, inputs, and outputs, respectively.SHDB and RRISL refer to the Social Hotspot and the Rubber research institute of Sri Lanka.

Figure 1 .
Figure 1.The framework of the study.Rectangles with rounded corners and ovals represent the processes, inputs, and outputs, respectively.SHDB and RRISL refer to the Social Hotspot database and the Rubber research institute of Sri Lanka.

Figure 2 .
Figure 2. System boundary (Cradle-to-gate) of the study.Shaded boxes demarcate background pro cesses.LDPE refers to low-density polyethylene.The main countries involved in the raw rubbe supply chain based in Sri Lanka are mentioned within parentheses (For more details, please refer to Tables S1-S4 in the Supplementary Material).

Figure 2 .
Figure 2. System boundary (Cradle-to-gate) of the study.Shaded boxes demarcate background processes.LDPE refers to low-density polyethylene.The main countries involved in the raw rubber supply chain based in Sri Lanka are mentioned within parentheses (For more details, please refer to Tables S1-S4 in the Supplementary Material).

Figure 3 .
Figure 3. Social footprints of three raw rubber types per 1 tonne of product basis in terms of medium risk hours equivalent (Mrheq).Contributions of respective impact categories to the social footprints of respective products are indicated within parentheses as percentages (%).RSS refers to ribbed smoked sheets.

Figure 3 .
Figure 3. Social footprints of three raw rubber types per 1 tonne of product basis in terms of medium risk hours equivalent (Mrheq).Contributions of respective impact categories to the social footprints of respective products are indicated within parentheses as percentages (%).RSS refers to ribbed smoked sheets.

Figure 4 .
Figure 4. Contribution of crepe-rubber supply chain activities at every subcategory.LDPE, MOP, and KIE refer to low-density polyethylene, muriate of potash, and kieserite.

Figure 4 .
Figure 4. Contribution of crepe-rubber supply chain activities at every subcategory.LDPE, MOP, and KIE refer to low-density polyethylene, muriate of potash, and kieserite.

Figure 4 .
Figure 4. Contribution of crepe-rubber supply chain activities at every subcategory.LDPE, MOP, and KIE refer to low-density polyethylene, muriate of potash, and kieserite.

Figure 6 .
Figure 6.Contribution of ribbed smoked sheets rubber supply chain activities at every subcategory.MOP and KIE refer to the muriate of potash, and kieserite, respectively.

Figure 6 .
Figure 6.Contribution of ribbed smoked sheets rubber supply chain activities at every subcategory.MOP and KIE refer to the muriate of potash, and kieserite, respectively.

Figure 9 .
Figure 9. Hotspots analysis of RSS supply chain ((a): Corruption; (b): Freedom of association & collective bargaining).Sectors with more than 3.0% contribution are labeled.Red text: x ≥ 10.0%; orange text: 10.0% > x ≥ 5.0%; green text: 5.0% > x ≥ 3.0%.Grey text signifies indirectly involved sectors.Sectors with less than 3.0% contribution are signified by bluish portions.For more details on hotpot sectors, see Tables S9 and S10 in the Supplementary Material.BLR, CHN, LKA, and IND refer to Belarus, China, Sri Lanka, and India.

Table 1 .
Social life cycle assessments on different product supply chains and the placement of our study.SLCA, PSILCA, and SHDB refer to the Social life cycle assessment, Product Social Impact Life Cycle Assessment, and Social hotspot database.

Table 2
encapsulates the social footprints of subcategories under each impact category in terms of Mrheq.Accordingly, the salient, highest risks are associated with Freedom of association & collective bargaining, followed by Corruption, Forced labor, Migrant labor, and the Legal system.'Unemployment' poses the smallest social risk of all subcategories.

Table 2 .
Social footprints of subcategories of each impact category under three rubber supply chains.CL and RSS refer to concentrated latex and ribbed smoked sheets, respectively.Values are given in Mrheq per 1 tonne of product basis with the percentage of contribution to the total in parenthesis.