Dose Response and Exposure Assessment of Household Hazardous Waste Dose Response and Exposure Assessment of Household Hazardous Waste

This study was conducted to assess the risk of health hazards to employees working in local authorities in Malaysia especially workforce involved in waste management. Therefore, the four steps process of Health Risk Assessment has been identified, which include hazard identification, exposure assessment, dose response assessment and risk characterization. It was estimated approximately 22,388 tons of wastes generated every year in Malaysia and around 2.2 % out of that amount were consisting of hazardous household waste (HHW) with mean average generation for each person per day was around 0.02 kg. The waste generation is expected to increase 2 to 3 % per year and estimated to reach approximately 31 million of tones per day in the year 2020. In this study, the household hazardous wastes (HHW) were analyzed for their permissible dose level and the existing hazard level, hazard index and cancer index. Cancer Index for dermal exposure is found to be 5.8 × 10– 7 mg/m 3 , for Inhalation dust 1.4× ×10– 1 mg/m 3 , which falls under Low Risk and for Inhalation aerosol is 5 × ×10– 2 mg/m 3 , under Medium Risk. Extra care must be taken for the management of HHW as if it is improperly managed, it will fall into High Risk.


Solid waste and household hazardous waste generation in Malaysia
Malaysia has undergone rather rapid urbanization since the beginning of the twentieth century and resulted in the development of more urban environment. Level of urbanization in Malaysia has increased from 26.8% in 1970 to 70.9% in 2010. Between 1970 and 2010, the urban population increased drastically by 557.5% or 16.5 million [1]. Modernization and progress has had their share of disadvantages, and one of the main aspects of concern is the pollution they are causing to human and environment. Increasing in the global population and the rising demand for food and other essentials such as household products lead to the increasing amount of waste being generated daily by each household and resulted in generation of more household hazardous wastes (HHW).
The total population of Malaysia in 2005 was only 25,048,000, and it increased gradually every year. Ministry of Housing and Local Government has reported that the estimated population of Malaysia in 2020 will be about 31,453,353 ( Table 1). The increase in population will directly contribute to the increase in waste too. Municipal Solid Waste (MSW) generation had increased to 6.0 million tons in 1998, with an average of 0.5-0.8 kg per capita per day. Per capita waste generalization increased from 0.70 kg/person in 1990s to 1.2 kg/person in 2000, but in the recent past the range has increased to between 0.5 and 2.5 kg/person. The production of domestic and commercial waste in 2000 was 8.0 million tons/year [2]. The estimated solid waste generation in Malaysia in 2007 was approximately 24,000 tons per day (8.64 million tons/year) for a population of approximately 26 million people, and only 70% of waste produced per day were collected [3]. It is known that the greater the economic prosperity of any nation, the higher the rate of urbanization and consequently the greater will be the amount of solid waste produced, and Malaysia is one of such nations. Moreover, as the population of Malaysia increases, the generation of HHW will also increase, where approximately 31 million tons per day are estimated by the year 2020. Increase in residents will increase the generation of wastes from time to time. If no efforts are taken to reduce the generation of wastes, it will contribute to the increase in HHW at landfill. As a result, it will impact the workers and public negatively. It will also contribute to ground water contamination. In addition, if there is open burning at the landfill, it will also lead to air contamination.

HHW composition in Malaysia
Determination of HHW composition was conducted at 40 local authorities in Malaysia. Results showed that a total of 9408 kg/day (0.02 kg/person/day) of HHW were generated. The category of cleaning products generated the highest portion of HHW of about 18%, followed by 16% of personal products, 12% of automotive products, 11% of fertilizers, 9% of paints and pesticides, 8% of lamps, 7% of stains and their removers, 6% of hobby products and batteries as the least generated HHW of about 5% (Figures 2 and 3).   From the study, it can be seen that the utilization of personal products and cleaning products is high in Malaysia and in line with the era of globalization and modernization process where plenty of these materials are available in the market. In general, it can be said that all the houses are generating HHW and each individual produces approximately about 0.02kg of HHW per day, and it is expected to rise about 2-5% per year. Without the waste minimization measures; "3Rs" and especially HHW waste separation at home, this will increase the waste disposal in landfills and increase the risk of health hazards to workers handling HHW and subsequently increase the occurrence of pollution.
The average generation of household hazardous waste (HHW) in Malaysia is 0.02 kg/p/day. Thus, for a population of 27 million, HHW waste generated will be about 7.3kg/p/year. Pesticides and batteries perhaps showed a small percentage but it could still cause harm to human. They may contaminate underground water and have the potential for causing cancer if not properly managed at local level.

Estimation of total HHW generated in Malaysia by 2020
Improper management of HHW will result in increasing of waste generation from time to time and contribute to health problems and pollution. The generation of HHW has been continuously on the rise and in Malaysia its management has been a problem till today due to its rapid increases in the volume and composition [2]. Improper disposal of HHW will lead to the contamination and pollution of river and underground water. The chemicals contained in HHW are hazardous and have the potential to cause cancer in people.

As shown in
This high generation of HHW in Malaysia is attributed to the rapid economic growth, population growth, developments of town and not forgetting the changing lifestyle that has been experienced in the recent past. If no action is taken to minimize waste in the early stages, it will harm the employees who are handling those waste materials that pollute our environment.

Dose response assessment
Garbage collection work is a major responsibility in all local authorities, and all types of waste, particularly domestic waste should be managed properly. Domestic waste contains HHW that need to be managed as efficiently as possible. Hazardous wastes at home are not subjected to the controlled scheduled waste according to the Environmental Quality Act, 1994, thus, the waste is directly disposed into the trash and then to the landfill. The absence of segregation at the source and landfill cause it to be potential water resources pollutant and direct exposure to workers. Improper management of HHW can directly expose the local authorities' workers to the above-mentioned hazard. Every employer must ensure that their employees are safe during the course of their duties as subjected in the provision of Occupational Safety and Health, 1994. Thus, to ensure the safety of workers, human health risk assessment should be conducted to identify the level of risk from HHW so that prevention and control measures can be applied and thus minimize the impact of health and safety of employees during the course of their duties.
Therefore, risk assessment for HHW must be conducted to estimate the increasing risk on health of human due to exposure to toxic substances. Four main steps involved in the process of assessing risks start from hazard identification, followed by exposure assessment, doseresponse assessment and end with risk characterization [4] as shown in Figure 4. Similar to solid waste management, HHW waste management includes all the activities starting from generation to the final disposal and is defined as the control, generation, storage, collection, transfer and transportation, processing and disposal of solid waste consistent with the best practices with public health and environmental considerations.
Toxicity of the chemicals present in HHW need to be studied in order to provide guidance for the workforce involved directly in the waste management process. Thus, the toxicity studies can be done through dose response assessment. Dose response assessment describes the toxicity of the chemicals identified in HHW using models based on human (including clinical and epidemiologic approaches) and animal studies, and data-based reference by US EPA integrated risk information system (IRIS).
The exposure assessment identifies exposed populations and details on the type, level, duration and frequency of exposure. Typically, exposure assessment consists of a number of steps [5] which are: i. Estimation of ambient air concentrations using air pollution monitor or other predictive air quality models, including analysis of spatial and temporal trends and distributions.

ii.
Identification of any special group that may be at risk due to high exposure (due to proximity, diet, or other factors) or vulnerability (due to pre-existing disease or other factor) to the pollutants. iii.
Development of appropriate exposure assumptions, for example activity factors (e.g. time spent outdoors), location factors (mobility), uptake factors (breathing rates, absorption rates, etc.), and other factors that may affect exposure to pollutants for each group.

iv.
Estimation of the number of exposed individual based on demographic and other data and validation of exposure analysis using monitoring or other means.

Empirical model of reference dose and exposure assessment of HHW
Referring to the provisions of the Occupational Safety and Health Act [6], the employer must take measures and precautions to prevent the employees from being exposed to safety and health hazards in their course of works. Thus, workers in local authorities involved in waste collection and disposal sites should be aware of the health hazards that exist so that they can be protected and reduce the risk of exposure to the HHW.
Workers and public have their right to know the requirement to inform particular group or individual on the health risk when exposed to HHW. Employers are required to assess chemicals contained in HHW or used in workplace and to make information regarding physical exposure and any associated risks of those agents to their employees. The ranking of the generated HHW, based on categories at City Council, is shown in Table 3.

Categories of HHW (g/person/day) (% by weight)
It can be seen that the cleaning products generated about 21 g/p/day, personal products 19 g/p/day, automotive 16 g/p/day, fertilizers 14 g/p/day and the rest less than 11 g/p/day. These high utilization figures are due to income disparities, social economic and cultural life of the population of the developed and growing city. These developments were in line with the use of hazardous household products (HHP) growing every day in the market. Overall generated HHW is 124 g/p/day. Therefore, these developments need to be addressed with the control measures in the management of solid waste and improve the management of HHW to ensure that the health of the workers is protected during the management of waste and the environment is not polluted by the HHW for the developed nation in 2020.
Moreover, it is important to highlight that, domestic wastes contain HHW and chemicals that can cause harm and affect health of human especially general workers who has direct contact with waste operations at dumping site or landfill. Therefore, an empirical model has been produced as given in Section 2.2 with different times and days of exposure at work equivalent with reference concentration (RfC) and reference dose (RfD) to serve as a guideline to employees or employers for minimization of health hazards. By knowing dose response of HHW to employees, preventive measures can be taken when carrying out these tasks.

Reference dose response of chemical contained in HHW
A dose-response relationship describes how the likelihood and severity of adverse health effects (the responses) are related to the amount and condition of exposure to an agent (the dose provided) [5]. Dose response assessments are determination of the relation between the magnitude of exposure and the probability of occurrence of the health effect in question [7][8][9][10]. It examines the relationship between the level of exposure and the resultant toxicity of the hazards. Therefore, establishment of a reference dose is an important aspect of the dose-response assessment. The RfD is the amount of the chemical, if received over a lifetime, that should not cause harmful effects. The RfD of a chemical is based on no observed adverse effect level (NOAEL) and lowest observable effect level (LOEAL) derived from a wide range of toxicity studies. The duration of exposure is important to consider. Varying durations of acute, short-term, intermediate-term and chronic are taken into account when formulating risk as a dose-response evaluation usually requires an extrapolation from the generally high doses administered to experimental animals, or exposures reported in occupational studies, to the exposures expected from human contact with the agent in the environment. There are many reasons for this. First, the possible mechanisms of all action for carcinogens are not fully understood [11,12]. NOAEL is the highest exposure level at which no statistically or biologically significant increases are seen in the frequency or severity of adverse effect between the exposed population and its appropriate control population. In an experiment with several NOAELs, the regulatory focus is normally on the highest one, leading to the common usage of the term NOAEL as the highest experimentally determined dose without a statistically or biologically significant adverse effect. In cases where a NOAEL has not been demonstrated experimentally, the term LOAEL is used, which this is the lowest dose tested [2].
By referring to RfC and RfD for each classes of HHW as shown in Table 4, for class I, the mean RfC is found to be 0.05 mg/m 3 and RfD is 0.17 mg/kg/day; for class II, RfC is 0.036 mg/m 3 , and RfD is 0.39 mg/kg/day; for class III, RfC is 0.0035 mg/m 3 and RfD is 0.017 mg/kg/day, for class IV, RfC is 0.002 mg/m 3 , and RfD is 0004 mg/kg/day, while for class V, RfD is 0094 mg/ kg/day and for class VI, RfC is 0.02 mg/m 3 and RfD is 0.60 mg/kg/day. These results indicated that the allowable HHW dose level for the RfC is 0.022 mg/m 3 , while that for RfD is 0.21 mg/kg/day. Exposure exceeding the dose limits specified here will cause risks and health hazards to workers exposed to it. Therefore, it is the responsibility of the employers to ensure that the allowable dose level of HHW is strictly followed so that the employees are not at risk of health hazards at workplace.

Average dose exposure of HHW
To determine the level of exposure to skin where HHW is in direct skin contact, the estimations were made, as given in Table 6. The estimate obtained from the average daily exposure dose (ADD) is 6.4 × 10 −8 µg/kg/day. Estimation was also made to determine the level of exposure to dust, as given in Table 7 and the average daily exposure dose (ADD) obtained is 1.35 × 10 −2 (0.0135) µg/kg/day. ADD obtained for exposure by inhalation for aerosol is found to be 5.6 × 10 −3 µg/kg /day ( Table 8). From these results, it can be concluded that if the rate of exposure exceeds the given levels, it can cause health hazards to workers either through the skin or through ingested or inhaled substances containing dangerous materials from HHW. Therefore, it is essential for the employer to know the minimum level of exposure and educate the employees. However, the minimum dose is very small and it difficult to prevent the workers from being exposed to this level. Hence, protection at work is very important, which can be done by providing PPEs to employees, such as gloves, uniforms and so on. What is more important is the knowledge and awareness among employees on the hazards that exist around them when performing their tasks.

Hazard risk and cancer risk index of HHW
To make estimation of hazard and cancer risk index, it is important and necessary to obtain the value of ADD exposure and the RFC or RfD for the estimations as shown in Tables 9 and 10.

ADD (exposure)
Average daily dose exposure Calculated cancer risk

Exposure by inhalation Aerosol
Average dose exposure daily (ADD) 5.6 × 10 −3 µg/kg/day Table 9. Value of ADD exposure for hazard risk.

Household Hazardous Waste Management
From these estimates, hazard risk index for HHW has been tabulated in Table 11 for some of the materials contained in the HHW that affect the health of both exposed workers and the public. The total hazard risk index for HHW was found to be more than 1. The estimations for cancer index are shown in Table 12. For benzene, the cancer index was found to be 5.8 × 10 −7 for exposure through the skin, 0.12 for dust inhalation exposure which is under low risk and 0.05 for aerosol inhalation exposure under medium risk, as well as for lead with hazard index of 9.6 × 10 −11 for exposure through skin, 2.0 × 10 −2 for dust inhalation and 8.4 × 10 −6 for aerosol inhalation. The total cancer index was less than the value of 1. Risk for dermal are acceptable to workers, however, if the risk can be resolved quickly and efficiently, control measures should be implemented and recorded. Medium risk requires a planned approach to control the hazard and applied temporary measures, if required.

Summary of short-term (1-hour) references concentration (RfC)
Table 13 shows the materials contained in the HHW that can pose hazards in terms of employee safety. Exposure to these materials should be limited or avoided to minimize the risk that occurs during the tasks, especially for garbage collecting employees and workers at the landfill. Exposure that occurs even in the short term will cause health hazards and adverse effects on them.  For materials found in solvents such as acetamide, exposure limit (1 hour) is 2.0 × 10 -5 mg/m 3 while for materials like allylchloride (varnish, perfume and insecticides); calcium cyanamide (fertilizer, herbicide, fungicide and pesticides), the permissible dose is 3 mg/m 3 . Exposure data should be communicated to employees and thus, safety and protection equipment and personal protective equipment can be provided by the employer and used solely by employees to reduce workplace accidents and health hazards.

Summary of long-term (chronic) exposure limit for human receptors
Based on  Above values showed that the solvent material is highly sensitive and hazardous because the dose limit allowed has the smallest value compared to other hazardous materials, in which it can cause risk to health, followed by the bulbs, batteries and paint. Therefore, these materials should be given priority for a more orderly management in each local authority in Malaysia.

Conclusion
The increasing scale of economic activity, urbanization, industrialization, rising standard of living and population growth has led to a sharp increase in the quantity of the generated waste. It can be said that almost every household is producing hazardous wastes as HHW is a part of domestic waste. Moreover, many fail to realize that the ingredients of some of the products that they use in their daily routine in house contain hazardous substances. Generally, out of the total solid waste generated, 64.7% ended up in the garbage bin, 27% are disposed down the drain and 2.4% are burnt while remaining 20.2% are disposed of by other means such as burying [13]. Improper use, storage and disposal of hazardous household products can harm humans and contaminate the environment [14]. Therefore, extra care must be taken when disposing used hazardous products as it can harm sanitation workers if thrown in with regular trash. Exposure to chemicals contained in some of the waste products in our home can cause health problems where the effects can range from minor problems such as watery eyes and irritation to skin to more serious problems such as poisoning, burns or may even lead to cancer. The exposures can be through ingestion by swallowing the hazardous substances if it is accidentally transferred onto food or cigarettes, through inhalation by breathing dust or fumes or through contact with skin or eye.
Referring to the flow chart in Figure 5, the work process undertaken would contribute to the potential hazards of exposure to garbage collection workers and in landfills if HHW existed in the operation during the handling. HHW disposal directly into the public dustbin and no separation at source caused nearly 80% of HHW disposed in the trash and then to the landfill. This is repeated when each truck at least run the collection for two to three trips a day. This situation will increase the potential of chemical exposure to the employees. The workers who do not practise health care and has no knowledge of the health hazards are more vulnerable and coupled with their lack of safety clothing such as gloves and safety helmets can hamper their safety and health.
In this case, employers must provide adequate training to staff regarding exposure to chemical hazards, toxic residues that affect the health and potentially cause cancer. The employers should provide adequate and appropriate personal protection equipment (PPE) to avoid direct exposure to workers during the work carried out. Preventive controls should also be done on a few trucks to transport the waste to prevent leakage of waste water from the garbage during operation and should provide covered and comfortable lorries for the workers.
Cases of accident and health can be prevented from occurring and recurring by adopting the concept of ergonomic principles in the management of solid waste, especially hazardous waste at home and steps like the separation at source is the best way to reduce exposure of workers to the HHW and prevent pollution in all local authorities in Malaysia.

Recommendation
The result from this study showed that HHW can affect humans. Hazardous household products most likely to contribute significantly to the input of hazardous substances were then identified as being the most problematic for the current waste management and disposal routes, namely paints, pesticides, arsenic treated wood and fluorescent lamps. Therefore the wastes must be properly managed. Separation of HHW at an early stage at home, such as separating HHW in separate plastic bags to reduce and minimize the waste dumping directly into public trash bin and eventually to the landfill must be practiced by all local authorities in Malaysia. A study on reviewing compliance with the provisions of OSHA, 1994 is necessary to ensure the implementation of the welfare, safety and health of employees in local authorities in Malaysia. Employees need to know the level of risk that exists in the workplace so that prevention and control measures can be carried out. Research also needs to be done for compliance with the labelling of hazardous products used at home in terms of their content of hazardous materials to serve as guidance and revisions for the consumers and facilitate local authorities in implementing the HHW collection program. The local authorities are proposed to play a more active role in the safety and security of workers with preventive measures; either by administrative or engineering and the usage of personal protective equipment among workers in local authorities should be strictly enforced, in an effort to improve and create a comfortable and safe workplace.
Therefore, the results of this study and recommendation can be used to increase and improve the management of solid waste in order to minimize health hazards and safety risks among workers, and surveillance. This chapter can be a guideline for proper management especially in HHW at local authorities in Malaysia.
Proper management of HHW will enhance the comfort of living and solve the problem of pollution of the earth and water resources that affect sources for drinking, and also overcome the air pollution due to open and uncontrolled burning. The contamination of groundwater due to improper disposal of HHW will continue if no concrete steps are taken by local authorities as well as the Ministry of Housing and Local Government to ensure that disposal sites are secure and proper management of waste is being practiced. Apart from that, human health risk assessment of HHW is important in determining the safety and health of employees and the public security and reduces the danger of existing risks. The contribution from proper management of HHW will make the management of solid waste more robust and ensure the comfort and health improved in line with community aspirations towards a developed nation by 2020.