The effect of distance on risk perception towards waste incineration plants: a comparison between local residents living within 0–3 km versus 3–8 km in Dongguan, Southern China

Waste incineration is becoming the dominant method of waste disposal globally, including in China. Local residents are concerned about the potential negative impacts of waste incineration plants (WIPs) on their environment and health. This study aimed to measure the differences of risk perception of local residents living within 0–3 km versus those living 3–8 km distant from a WIP and explore other factors associated with risk perception. A cross-sectional study was conducted in communities surrounding three municipal WIPs in Dongguan, China. Of 881 residents randomly selected, 454 lived within 0–3 km and 427 lived 3–8 km from their local WIP. Differences in risk perception between the two groups and factors associated with risk perception were analyzed using multivariable logistic regression. Seventy percent of the residents reported a high overall risk perception towards the WIPs. Overall risk perceptions, perceived health effects, and psychological stress domains were not significantly different between those living within 0–3 km and 3–8 km groups after adjusting for other variables. The effect of distance on risk perception was modified by social trust, as the study found that those in the 0–3 km group having low social trust had significantly higher risk perception. Gender, marital status, housing type, and duration of residence were independently associated with risk perception. Social trust is an important factor in alleviating the residents’ risk perceptions towards a WIP, and is further affected by the distance from the WIP. It is essential for WIP governors to provide accurate information about WIPs to their residents along with good quality control.


Introduction
Rapid economic development and urbanization have been expanding worldwide and together create huge amounts of waste which require treatment and disposal.Global waste is expected to increase by 70%, from 2.01 billion tons of waste in 2016 to 3.40 billion tons in 2050 (Kaza et al 2018).As the largest developing country, China has had a large growth of municipal solid waste in the past 15 years, from 152 million tons in 2007 to 248 million tons in 2021(Ministry of Housing and Urban-Rural Development of the Peoples' Republic of China 2022).There are three main ways of disposing of waste in China, namely landfills, incineration and composting.Due to a scarcity of land and secondary pollution from landfills, many scientists believe that incineration is the best option (Kalyani andPandey 2014, Cucchiella et al 2017) and waste incineration has become the dominant method of waste disposal in China (Ministry of Housing and Urban-Rural Development of the Peoples' Republic of China 2022).
Waste incineration plants (WIPs) have traditionally been associated with emission of toxic pollutants; however, the current generation of WIPs is far less polluting and more energy efficient than earlier types.Although the available scientific evidence suggests that actual health threats to the general public from the operation of WIPs are unlikely (Nadal et al 2020), the perception of risk from WIPs among the general population, particularly in communities surrounding such facilities, is high (Ren et al 2016).The acceptance of or resistance to WIPs depends on social and public perceptions on the effects of these facilities to their local environment and safety, a phenomenon known as 'not in my backyard' (NIMBY), and the negative effects of such NIMBYs are influenced by prior public information (Li andLi 2021, Liu et al 2021).
A recent study found that residents living near WIPs reported negative consequences on physical health, psychological stress, neighborhood image property values and environment (Kim et al 2022).Janmaimool and Watanabe (2014) suggested that the perceptions of environmental risk can be influenced by a wide range of psycho-sociological factors.Another study found that the residents who perceived high benefits from WIPs had a lower perception of the risks they faced (Huang and Zhang 2019).Public trust and confidence in the institutions and persons who were responsible for controlling hazardous effects and managing risk (Hou et al 2019, Lee 2018), and the decision-making process concerning location and operation of waste facilities (World Health Organization Regional Office for Europe 2007) were reported to be factors associated with residents' risk perceptions.Previous studies also found that socio-demographic characteristics may be associated with risk perception (McCright and Xiao 2014, Guo et al 2018, McIntyre et al 2018, Subiza-Pérez et al 2020).
The spatial distance from a WIP is a key factor affecting the risk perceptions of local residents (Zhou et al 2022), and a study in Portugal found that residents living closer to a WIP site had higher risk perceptions in mental health aspects (Lima 2004).This can be explained through residents being less satisfied with the local environmental conditions and being aware of pollution (Lee et al 2012), or higher concern about natural hazards, anthropogenic hazards, and waste management in residents living near a WIP (Bena et al 2019).However, another study in Spain did not find a significant difference in perceived risk between those living within 10 km of a WIP versus those living farther away (Subiza-Pérez et al 2020).
The study hypothesized that the residents living closer to a WIP would have higher perceptions of risk than those living further away and the risk perceptions were also related to the trust on the responsibility of controlling hazard and environmental risk in the community and other factors (Janmaimool and Watanabe 2014).From previous studies above, there were different risk perception towards WIP in different distances depending on country contexts and there have been few studies examining risk perception (Liu 2002, Lin et al 2018), even though there are currently 583 WIPs operating in China.Therefore, this study aimed to measure the differences of risk perception between local residents living within 0-3 km versus those living 3-8 km distant from a WIP and explore other factors associated with risk perception.

Study design and settings
A cross-sectional study was conducted in communities surrounding three municipal WIPs in Dongguan, China during 28 November 2021 to 1 July 2022.Dongguan is a prefecture-level city in central Guangdong province, China.With rapid urbanization and population growth, Dongguan generated 4.49 million tons of municipal solid waste in 2019, ranking ninth among all cities in China.Consequently, the Dongguan government addressed the challenging issue by establishing four waste incineration plants.These four WIPs can handle about 4.09 million tons of waste annually, accounting for 91.09% of the generated waste.Three of these WIPs were selected for the study to assess the risk perceptions of local residents, namely Urban WIP, Hengli WIP, and Machong WIP, which lie respectively in Nancheng District, Hengli Town, and Machong Town in Donguan.These three WIPs can incinerate 3.61 million tons of waste per year, accounting for 80.40% of Dongguan municipal solid waste.These three WIPs were chosen for this study as they are in close proximity to populated areas and can potentially affect local residents.

Study sample and sampling
Residents aged 18 years or above who had lived within an 8 km radius of one of the three municipal WIPs for at least half a year were included in the overall study population.In order to explore whether there were differences in risk perception among residents living at different distances from the WIP, the residents were divided into two groups according to their distance from the WIP, with closer and further than 3 km as the separating value (Lung et al 2020), resulting in a 0-3 km group and a 3-8 km group.As there were no previous studies regarding low-or high-risk perceptions related to WIPs, we estimated a 10% difference of risk perceptions between the 55% of residents living in the 0-3 km areas and the 45% of those living in the 3-8 km areas.The required sample size was calculated using the formula for the difference of two proportions with a continuity correction, 95% confidence interval, and 80% power, resulting in at least 412 residents being required in each group.According to the distribution diagram of environmentally sensitive spots within 3 km of WIPs published by the Dongguan Environmental Protection Authority, this study chose 3 km as the cut-off point and the limit of 8 km was chosen as the furthest distance to avoid overlapping areas across the three studied WIPs.

Variables and measurements
The main outcome measure in this study was risk perception which was measured using the respondent's level of agreement with each of five domains regarding environmental pollution (The WIP can produce environmental pollution), health effects (The WIP affects my health), psychological stress (The WIP causes psychological stress for me), neighborhood image (The WIP damages the neighborhood's image) and damage to property (The WIP reduces property values) recommended from previous studies (Lima 2004, Kim et al 2022).Each domain was measured on a 5-point Likert scale ranging from 'strongly disagree' scored as 1 to 'strongly agree' scored as 5 (where higher scores reflect higher risk perception).The reliability of all domains to reflect risk perception was pretested on 30 residents from each distance from the WIP to assess the internal consistency which showed good reliability (Cronbach's alpha 0.92, 95%, confidence interval 0.89-0.93).
The main exposure of interest was distance, which was divided into two categories: 0-3 km and 3-8 km from a WIP.Other independent variables were sociodemographic characteristics, benefit perception, social trust, and decision-making process.Sociodemographic characteristics were comprised of 7 items (gender, age, marital status, education level, annual personal income, housing type, and duration of residence).Income in yuan was calculated in USD using an exchange rate of 0.16.
The benefit perception of the WIPs was assessed on a 5-item Likert scale, with responses ranging from strong disagreement to strong agreement on a scale of 1 to 5 (where higher scores reflect higher benefit perception).The five items were job opportunities, waste reduction, energy supply, infrastructure renewal and subsidies.The internal consistency of these five items was good (α = 0.81, CI 0.76-0.85).The total mean of these five items was calculated for further analysis.Social trust was assessed with five items including strict regulation, emission standards, incineration technology, expert's views and media coverage.All five items were measured on a 5-point Likert scale, with higher scores indicating higher social trust.The internal consistency of these five items was very good (α = 0.91, CI 0.89-0.93).Again, the total mean of these five items was calculated for subsequent analysis.Decision-making process was measured by one question: 'Do you think the decision to locate WIPs is democratic and open?'The response was on a 5-point Likert scale from 1 to 5 where 1 indicated strongly disagree, 5 strongly agree.

Data collection 2.4.1. Preparatory phase
Before the field data collection, the principal investigator and researchers visited the planned study area and created a simple geographic information system map to understand the household situations within an 8 km radius of the study WIPs and identified the households of the residents living in 0-3 km and 3-8 km areas from a WIP.The research assistants were trained by the principal investigator on providing research information, objectives, and the process of data collection for conducting household visits.The researchers initially contacted the village or neighborhood committees to inform them of the study and get their support and approval, and these committees then informed the residents that a research team would visit them at their homes.

Data collection phase
The research team visited the households in each area of which the first household was randomly selected and further houses were consecutively approached until the required sample size was reached.At each household, the household head was informed of the study and invited to participate, and if they agreed their verbal consent was recorded.The data were collected using a structured questionnaire through a self-administered or interview approach depending on the resident's level of literacy, in a private area where their responses were confidentially recorded.

Data management and statistical analysis
Data were entered in Epidata v3.1 by double entry and analyzed using R v4.1.3(R Core Team 2022).The Likert scores were categorized into binary scales, 1-3 as low-risk perception and 4-5 as high-risk perception.Overall risk perception was calculated by summing the scores of all domains divided by five and then categorized into the binary scale using a cut-off value of 3 as indicating low-and high-risk perceptions.The data of benefit perception, social trust, and decision-making process were managed in the same way.
The information of sociodemographic characteristics, benefit perception, social trust, and decision-making process of the study residents are descriptively presented using percentages.The differences of all variables by distance groups were analyzed using the Chi-square test.The factors associated with overall risk perception and significant domains of risk perception were tested by multivariable logistic regression regarding the effect modification of significant variables on the distance.Variables with a p value below 0.2 in univariate analysis were selected to use in the first model of multivariable logistic regression.The crude odds ratio (OR) and adjusted odds ratio (Adj.OR) with 95% confidence interval (CI) were used and a p value of 0.05 was considered as significant.When an effect modification was identified, the stratification results regarding the effect modifier were analyzed (Knol and VanderWeele 2012) using the InteractionR package (Alli 2021).
Risk perceptions by distance from the nearest WIP are shown in table 2. For overall risk perception, approximately 70% of the residents agreed that the local WIP posed a risk to them, with more residents in the 0-3 km group having a high overall risk perception than in the 3-8 km group, but significance was not found (71.6% versus 68.4%, p = 0.300).Among the five individual domains, high risk perceptions were more likely to be found in the domains of environmental pollution (67.2%), health effects (63.7%), and damage to property (56.8%).The domains of health effects and psychological stress were significantly different between the 0-3 km and 3-8 km groups.For analysis of factors associated with risk perception, apart from overall risk perception, the significant domains of health effects and psychological stress were selected for further regression analysis.
Table 3 shows the factors associated with overall risk perception towards the WIPs.Without interaction terms in the model 1, the distance from the WIP was not significantly associated with overall risk perception.Female residents, those living in purchased houses, and those with low social trust had higher overall risk perceptions of WIPs.For model 2 with the interaction between distance and social trust, the significance of housing type disappeared.Female residents also had higher odds of high-risk perception compared with male residents.A significant interaction effect between distance and social trust was found.
Table 4 shows the modification of the effect of distance on overall risk perception towards the WIPs by social trust.Compared with residents in the 3-8 km group with high social trust, only those in the 0-3 km group with low social trust had significantly higher odds of high-risk perception (Adj.OR 2.35, 95% CI 1.54-3.57)adjusted for gender and housing type.The effect of distance in the high social trust group tended to be protective but insignificant, whereas the odds ratio among those in the low social trust group was 1.68 (95% CI 1.08-2.59).
Table 5 presents the factors associated with perceived health effects in the final multivariable logistic regression model.The risk perceptions of health effects were not significantly different between the 0-3 km and 3-8 km groups.Females, married residents or those with low social trust had higher perceived health effects of the WIPs in model 1 without interactions.The interaction effect between distance and social trust was significant.Table 6 describes the modifications of the effect of distance on perceived health effects towards the WIP by social trust.Compared with residents in the 3-8 km group with high social trust, only those in the 0-3 km group with low social trust had significantly higher odds of high-risk perceptions (Adj.OR 3.10, 95% CI 2.06-4.67)adjusted for gender and marital status.Among those in the low social trust group, the odds of risk perception on health effects were higher in the 0-3 km group than in the 3-8 km group (Adj.OR 2.11, 95% CI 1.39-3.20).
Table 7 shows the results of factors associated with the psychological stress domain.No significant association between distance and psychological stress was observed.Residents who were married, those having a purchased house, and those with low social trust had a higher risk perception of psychological stress.The duration of residence near the WIP had a negative dose response to psychological stress, that is, the longer the resident had lived near the WIP, the less psychological stress.There was a significant interaction between distance and social trust on psychological stress.The modification of the effect of distance on psychological stress towards the WIP by social trust is shown in table 8.The odds ratios of risk perception on psychological stress of residents with low social trust in the 0-3 km (Adj.OR 3.91, 95% CI 2.66-5.76)and 3-8 km (Adj.OR 1.90, 95% CI 1.27-2.83)groups were higher compared with those with high social trust and in the 3-8 km group.Residents living closer had higher psychological stress than those living farther away in the low social trust group (Adj.OR 2.06, 95% CI 1.41-3.01),but a non-significant inverse opposite findings was found in the high social trust group (Adj.OR 0.75, 95% CI 0.49-1.17).

Discussion
Residents living within 3 km of their local WIP had higher perceptions of adverse health effects and psychological stress from the WIP than those living 3-8 km distant.No significant differences of overall risk perception, health effects and psychological stress were found between the two distance groups after adjusting with other variables in multivariate analysis.Social trust was a significantly independent factor for risk perception and constantly interacted with distance when assessing all other factors.Compared with residents in the 3-8 km group with high social trust, those in the 0-3 km group with low social trust had significantly higher odds of risk perception.The effect of distance within the strata of social trust showed higher odds of risk perception in the low social trust group.Gender, marital status, housing type, and duration of residence were independently associated with risk perception.
Most residents in our study reported high overall risk perception towards the WIPs regardless of the distance, which was consistent with the findings of previous studies even though the methods of risk perception measurement were different in studies from Italy and Spain (Bena et al 2019, Subiza-Pérez et al 2020).This may be explained through the nature of human response for high uncertainty related to the dynamics of environments (Osman 2010).For the effect of distance on risk perception, there were no standard cut-off points, thus we chose the 0-3 km and 3-8 km distances based on a previous study (Lung et al 2020) which had a reasonable geographic distribution of three studied WIPs.We found significant differences of risk perception on health effects and psychological stress between the two distance groups which was similar to previous studies that used different cut-off points conducted in Korea using univariate analysis (Lee et al 2012, Kim et al 2022).No significant differences of overall risk perception, health effects or psychological stress between the two distance groups were observed in our study after adjusting for other variables.The null effect of distance was shared by two previous studies conducted in China which found that the relationship between overall risk perception level and distance was not statistically significant (Liu 2002, Lin et al 2018).It may be assumed that other factors in the model were more influential and a habituation effect for residents living near a WIP leads to lower levels of risk perception (Greenberg 2009).In contrast, studies conducted in Portugal and Italy found that people who lived near a WIP had higher overall risk perceptions than those who lived farther away from a WIP, but these studies did not assess the effect of distance on perceived health effects and psychological stress (Lima 2004, Bena et al 2019).
Social trust, in our study, was significantly associated with overall risk perception, health effects, and psychological stress towards WIPs.Two previous studies found that residents with low social trust had increased risk perception (Lee 2018).This may be explained by noting that local residents had limited information on the potential hazards and new technologies of WIP and they relied on social trust to reduce the complexity and uncertainty they were faced with (López-Navarro et al 2013).A review in Hong Kong also reported the challenges of establishing sustainable waste management from the lacks of foresight and planning and auxiliary waste management technology, and the limited capacity to recycle (Fabian and Lou 2019).Trust and social justice can be strengthened by improving public communication, increasing information transparency by resident's on-site visit to WIPs, conducting quality monitoring, and compensation policy (Lu 2023).In addition, social license to operate to enhance the trust on WIP has been widely reviewed recently and reported that it was still questionable and suggested further studies (Lehtonen et al 2022).A study conducted among the residents in four cities in China living within 3 km from WIPs found that social license to operate was applicable for WIP management, but the enhancing social trust was still controversial (He et al 2023).Social trust was found in our study to be an effect modifier on the relationship of distance and risk perception, indicating the association between distance and risk perception may be different depending on the level of social trust.The findings of our study that residents living within 0-3 km with low social trust had higher risk perception than those living 3-8 km away with high social trust, which supports the concept of the NIMBY syndrome (Dear 1992).A qualitative study in China found positive views between governments and citizens and the importance of perceived justice and political efficacy.WIPs are usually opposed by the public as they are perceived to be NIMBY facilities but this qualitative study did not test the hypothesis of distance because all respondents were the residents near WIPs (Zhang et al 2021).A study in northern China also found that trust towards WIPs among the residents living in the vicinity of WIPs was a significant factor influencing residents' perceptions (Huang et al 2022).We could not find any previous studies assessing the effect modification of social trust between distance and risk perception.We found one previous study considering social acceptance of WIPs in China tested the effect modification of trust on the relationship between risk perception and anti-incinerator sentiment (Hou et al 2019), not between distance and risk perception as in our study.
The finding that females had a higher overall risk perception of WIPs than males was consistent with the information from two literature reviews on risk perceptions (McCright and Xiao 2014, Subiza-Pérez et al 2020).This may be because females were also found to be more likely to worry about health risks compared to males (Couch and Coles 2011).Likewise, we found that being married increased risk perceptions on health and psychological stress, which was consistent with the findings of previous studies conducted in the UK and China (McIntyre et al 2018, Chen et al 2022).A possible explanation could be that married couples are more concerned about their parents or children residing with the family leading them to be more worried about the future health impacts of WIPs for their family.
People who owned their own houses through purchase reported greater overall risk perception and psychological stress than renters, which was opposite to a previous study (McIntyre et al 2018).This may be explained by suggesting that local residents who bought houses thought that a WIP would damage the value of their communities, making it harder for them to sell their homes and move elsewhere, compared with renters.Similarly, residents who lived near a WIP for longer durations had lower risk perceptions on psychological stress.This is in line with another study which suggested that longer lengths of residence may provide confidence in navigating neighborhood risks and increase feelings of safety (Guo et al 2018).This result may be explained by the fact the length of residence is the best predictor of place attachment, which reduces local residents' psychological stress in their neighborhood (Anton andLawrence 2014, McIntyre et al 2018).
There have been few studies assessing the risk perception of local residents towards WIPs which have been in operation in local communities of China ranging from 5 years to more than a decade.We used the analysis of effect modification of other independent variables on the relationship of distance and risk perception towards WIPs, which showed residents with low social trust had a strong NIMBY syndrome.
The study had some limitations.First, our study included only residents who currently lived in the study setting, which may have introduced residential self-selection issues as some residents may have moved to other places if they felt discomfort about the nearby WIP.Second, to achieve sufficient statistical power concerning the sample size of the residents, we included three WIPs due to the small number of residents living close to each WIP.These three WIPs had some different characteristics, such as stack height, local atmospheric conditions and topographic situation; however, such conditions may not be recognized by residents and thus may not have influenced their risk perception.Third, we asked about the perception of the risk specifically towards WIPs, without including other sources of pollution.Although there are other factories in the study areas, we emphasized to the residents we wanted their perceptions of the WIP in their area in our questionnaire.Finally, this was a cross-sectional study in which the causality between a WIP and risk perception on local residents could not be confidently tested.
We found that social trust was an important factor to alleviate a resident's risk perception towards WIPs and was related to the distance the resident lives from the WIP.Accurate information about WIPs by the WIP managers to improve social trust is essential for residents who live near a WIP.Effective risk communication, providing information transparency, and introducing long-term monitoring of the environmental and health effects of WIPs on nearby residents to enhancing social trust require further study.In addition, expanded surveys to include a greater number of WIPs with various characteristics, topographic situations and other sources of pollution will be useful for future policy planning on waste management.

Conclusion
This study highlighted the effect modifications of social trust on the relationship between the resident's distance from WIPs and overall risk perception, health effects and psychological stress.Enhancing strict regulation, emission standards, incineration technology, expert's views and media coverage is important for making resident's social trust.The study on strengthening the social trust on WIPs particularly among the residents nearby WIPs is required to lower perception of risk towards WIPs, especially health effects and psychological stress along with the need of generating and operating WIPs in the future.

Table 1 .
Sociodemographic characteristics, benefit perception, social trust, and decision-making process of study residents by distance from their WIP.

Table 2 .
Risk perception towards a WIP by distance.

Table 3 .
Final model of multivariable logistic regression for associated factors with overall risk perception towards WIPs.

Table 4 .
Modification of the effect of distance on overall risk perception towards WIPs by social trust.

Table 5 .
Final model of multivariable logistic regression for associated factors with health effect towards WIPs.

Table 6 .
Modification of the effect of distance on health effects towards WIPs by social trust.Measure of effect modification on multiplicative scale: ratio of ORs (95% CI) = 2.92 (1.62-5.24).Adj.ORs are adjusted for gender and marital status.WIPs: waste incineration plants.

Table 7 .
Final model of multivariable logistic regression for associated factors with psychological stress towards a WIP.

Table 8 .
Modification of the effect of distance on psychological stress towards WIPs by social trust.