Exposures to numerous substances designated by the International Agency for Research on Cancer (IARC) as known, probable and possible carcinogens may occur in pulp and paper operations. Asbestos, known to cause lung cancer and mesothelioma, is used to insulate pipes and boilers. Talc is used extensively as a paper additive, and can be contaminated with asbestos. Other paper additives, including benzidine-based dyes, formaldehyde and epichlorohydrin, are considered probable human carcinogens. Hexavalent chromium and nickel compounds, generated in stainless-steel welding, are known lung and nasal carcinogens. Wood dust has recently been classified by IARC as a known carcinogen, based mainly on evidence of nasal cancer among workers exposed to hardwood dust (IARC, 1995). Diesel exhaust, hydrazine, styrene, mineral oils, chlorinated phenols and dioxins, and ionizing radiation are other probable or possible carcinogens which may be present in mill operations.

Few epidemiological studies specific to pulp and paper operations have been conducted, and they indicate few consistent results. Exposure classifications in these studies have often used the broad industrial category “pulp and paper”, and even the most specific classifications grouped workers by types of pulping or large mill areas. The three cohort studies in the literature to date involved fewer than 4,000 workers each. Several large cohort studies are currently under way, and IARC is coordinating an international multicentric study likely to include data from more than 150,000 pulp and paper workers, allowing much more specific exposure analyses. This article will review the available knowledge from studies published to date. More detailed information may be obtained from earlier published reviews by IARC (1980, 1987, and 1995) and by Torén, Persson and Wingren (1996). Results for lung, stomach and haematological malignancies are summarized in table 1.

Table 1. Summary of studies on lung cancer, stomach cancer, lymphoma and leukaemia in pulp and paper workers

C = cohort study, CR = case-referent study, PM = proportionate mortality study.
* Statistically significant. ^§ = Where separately reported, NHL = non Hodgkin lymphoma and HD = Hodgkin’s disease. X = 0 or 1 case reported, no risk estimate calculated, — = No data reported.

A risk estimate exceeding 1.0 means the risk is increased, and a risk estimate below 1.0 indicates decreased risk.

Source: Adapted from Torén, Persson and Wingren 1996.

Respiratory System Cancers

Maintenance workers in paper and pulp mills experience an increased risk of lung cancer and malignant mesotheliomas, probably because of their exposure to asbestos. A Swedish study showed a threefold increased risk of pleural mesothelioma among pulp and paper workers (Malker et al. 1985). When the exposure was further analysed, 71% of the cases had been exposed to asbestos, the majority having worked in mill maintenance. Elevations in lung cancer risk among maintenance workers have also been shown in Swedish and Finnish pulp and paper mills (Torén, Sällsten and Järvholm 1991; Jäppinen et al. 1987).

In the same Finnish study, a twofold increased risk of lung cancer was also observed among both paper mill and board mill workers. The investigators made a subsequent study restricted to pulp mill workers exposed to chlorine compounds, and found a threefold increased risk of lung cancer.

Few other studies of pulp and paper workers have shown increased risks for lung cancer. A Canadian study showed an increased risk among those exposed to paper dust (Siemiatycki et al. 1986), and US and Swedish studies showed increased risks among paper mill workers (Milham and Demers 1984; Torén, Järvholm and Morgan 1989).

Gastro-intestinal Cancers

Increased risk of stomach cancer has been indicated in many studies, but the risks are not clearly associated with any one area; therefore the relevant exposure is unknown. Socio-economic status and dietary habits are also risk factors for stomach cancer, and might be confounders; these factors were not taken into account in any of the studies reviewed.

The association between gastric cancer and pulp and paper work was first seen in a US study in the 1970s (Milham and Demers 1984). The risk was found to be even higher, nearly doubled, when sulphite workers were examined separately. US sulphite and groundwood workers were also found in a later study to run an increased risk of stomach cancer (Robinson, Waxweiller and Fowler 1986). A risk of the same magnitude was found in a Swedish study among pulp and paper mill workers from an area where only sulphite pulp was produced (Wingren et al. 1991). American paper, paperboard and pulp mill workers in New Hampshire and Washington state ran an increased mortality from stomach cancer (Schwartz 1988; Milham 1976). The subjects were probably a mixture of sulphite, sulphate and paper mill workers. In a Swedish study, threefold increased mortality due to stomach cancer was found in a group comprising sulphite and paper mill workers (Wingren, Kling and Axelson 1985). The majority of pulp and paper studies reported excesses of stomach cancer, though some did not.

Due to the small number of cases, most studies of other gastrointestinal cancers are inconclusive. An increased risk of colon cancer among workers in the sulphate process and in paper board production has been reported in a Finnish study (Jäppinen et al. 1987), as well as among US pulp and paper workers (Solet et al. 1989). The incidence of biliary tract cancer in Sweden between 1961 and 1979 was linked with occupational data from the 1960 National Census (Malker et al. 1986). An increased incidence of cancer of the gallbladder among male paper mill workers was identified. Increased risks of pancreatic cancer have been observed in some studies of paper mill workers and sulphite workers (Milham and Demers 1984; Henneberger, Ferris and Monson 1989), as well as in the broad group of pulp and paper workers (Pickle and Gottlieb 1980; Wingren et al. 1991). These findings have not been substantiated in other studies.

Haematological Malignancies

The issue of lymphomas among pulp and paper mill workers was originally addressed in a US study from the 1960s, where a fourfold increased risk of Hodgkin’s disease was found among pulp and paper workers (Milham and Hesser 1967). In a subsequent study, the mortality among pulp and paper mill workers in the state of Washington between 1950 and 1971 was investigated, and a doubled risk of both Hodgkin’s disease and multiple myeloma was observed (Milham 1976). This study was followed by one analysing mortality among pulp and paper union members in the United States and Canada (Milham and Demers 1984). It showed almost a threefold increased risk for lymphosarcoma and reticulum cell sarcoma among sulphite workers, while sulphate workers had a fourfold increased risk of Hodgkin’s disease. In a US cohort study, sulphate workers were observed to have a twofold risk of lymphosarcoma and reticulosarcoma (Robinson, Waxweiller and Fowler 1986).

In many of the studies where it was possible to investigate the occurrence of malignant lymphomas, an increased risk has been found (Wingren et al. 1991; Persson et al. 1993). Since the increased risk occurs both in sulphate and sulphite mill workers, this points towards a common source of exposure. In the sorting and chipping departments, the exposures are rather similar. The workforce is exposed to wood dust, terpenes and other extractable compounds from the wood. In addition, both pulping processes bleach with chlorine, which has the potential to create chlorinated organic by-products, including small amounts of dioxins.

Compared with lymphomas, studies on leukaemias show less consistent patterns, and the risk estimates are lower.

Other Malignancies

Among US paper mill workers with presumed exposure to formaldehyde, four cases of urinary tract cancer were found after 30 years’ latency, although only one was expected (Robinson, Waxweiller and Fowler 1986). All of these individuals had worked in the paper-drying areas of the paper mills.

In a case-control study from Massachusetts, central nervous system tumours in childhood were associated with an unspecified paternal occupation as a paper and pulp mill worker (Kwa and Fine 1980). The authors regarded their observation as a random event. However, in three subsequent studies, increased risks were also found (Johnson et al. 1987; Nasca et al. 1988; Kuijten, Bunin and Nass 1992). In studies from Sweden and Finland, two- to threefold increased risks of brain tumours were observed among pulp and paper mill workers.

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Because the pulp and paper industry is a large consumer of natural resources (i.e., wood, water and energy), it can be a major contributor to water, air and soil pollution problems and has come under a great deal of scrutiny in recent years. This concern appears to be warranted, considering the quantity of water pollutants generated per tonne of pulp (e.g., 55 kg of biological oxygen demand, 70 kg of suspended solids, and up to 8 kg of organochlorine compounds) and the amount of pulp produced globally on an annual basis (approximately 180 million tonnes in 1994). In addition, only about 35% of used paper is recycled, and waste paper is a major contributor to total worldwide solid waste (about 150 million of 500 million tonnes annually).

Historically, pollution control was not considered in the design of pulp and paper mills. Many of the processes used in the industry were developed with little regard for minimizing effluent volume and pollutant concentration. Since the 1970s, pollution abatement technologies have become integral components of mill design in Europe, North America and other parts of the world. Figure 1 illustrates trends over the period 1980 to 1994 in Canadian pulp and paper mills in response to some of these environmental concerns: increased use of wood waste products and recyclable paper as fibre sources; and decreased oxygen demand and chlorinated organics in wastewater.

Figure 1. Environmental indicators in Canadian pulp and paper mills, 1980 to 1994, showing use of wood waste and recyclable paper in production, and biological oxygen demand (BOD) and  organochlorine compounds (AOX) in wastewater effluent.

This article discusses the major environmental issues associated with the pulp and paper process, identifies the sources of pollution within the process and briefly describes control technologies, including both external treatment and in-plant modifications. Issues arising from wood waste and anti-sapstain fungicides are dealt with in more detail in the chapter Lumber.

Air Pollution Issues

Air emissions of oxidized sulphur compounds from pulp and paper mills have caused damage to vegetation, and emissions of reduced sulphur compounds have generated complaints about “rotten egg” odours. Studies among residents of pulp mill communities, in particular children, have shown respiratory effects related to particulate emissions, and mucous membrane irritation and headache thought to be related to reduced sulphur compounds. Of the pulping processes, those with the greatest potential to cause air pollution problems are chemical methods, in particular kraft pulping.

Sulphur oxides are emitted at the highest rates from sulphite operations, especially those using calcium or magnesium bases. The major sources include batch digester blows, evaporators and liquor preparation, with washing, screening and recovery operations contributing lesser amounts. Kraft recovery furnaces are also a source of sulphur dioxide, as are power boilers which use high-sulphur coal or oil as fuel.

Reduced sulphur compounds, including hydrogen sulphide, methyl mercaptan, dimethyl sulphide and dimethyl disulphide, are almost exclusively associated with kraft pulping, and give these mills their characteristic odour. The major sources include the recovery furnace, digester blow, digester relief valves, and washer vents, though evaporators, smelt tanks, slakers, the lime kiln and waste water may also contribute. Some sulphite operations use reducing environments in their recovery furnaces and may have associated reduced sulphur odour problems.

Sulphur gases emitted by the recovery boiler are best controlled by reducing emissions at the source. Controls include black liquor oxidation, reduction in liquor sulphidity, low-odour recovery boilers and proper operation of the recovery furnace. Sulphur gases from digester blow, digester relief valves and liquor evaporation can be collected and incinerated - for example, in the lime kiln. Combustion flue gases can be collected using scrubbers.

Nitrogen oxides are produced as products of high-temperature combustion, and may arise in any mill with a recovery boiler, power boiler or lime kiln, depending on the operating conditions. The formation of nitrogen oxides can be controlled by regulating temperatures, air-fuel ratios and residence time in the combustion zone. Other gaseous compounds are minor contributors to mill air pollution (e.g., carbon monoxide from incomplete combustion, chloroform from bleaching operations, and volatile organics from digester relief and liquor evaporation).

Particulates arise mainly from combustion operations, though smelt-dissolving tanks can also be a minor source. More than 50% of pulp mill particulate is very fine (less than 1 μm in diameter). This fine material includes sodium sulphate (Na₂SO₄) and sodium carbonate (Na₂CO₃) from recovery furnaces, lime kilns and smelt-dissolving tanks, and NaCl from burning by-products of logs which have been stored in salt water. Lime kiln emissions include a significant amount of coarse particulates due to entrainment of calcium salts and sublimation of sodium compounds. Coarse particulate may also include fly ash and organic combustion products, especially from power boilers. Reduction of particulate concentrations can be achieved by passing flue gases through electrostatic precipitators or scrubbers. Recent innovations in power boiler technology include fluidized bed incinerators which burn at very high temperatures, result in more efficient energy conversion, and allow burning of less uniform wood waste.

Water Pollution Issues

Contaminated wastewater from pulp and paper mills can cause death of aquatic organisms, allow bioaccumulation of toxic compounds in fish, and impair the taste of downstream drinking water. Pulp and paper wastewater effluents are characterized on the basis of physical, chemical or biological characteristics, with the most important being solids content, oxygen demand and toxicity.

The solids content of wastewater is typically classified on the basis of the fraction that is suspended (versus dissolved), the fraction of suspended solids that is settleable, and the fractions of either that are volatile. The settleable fraction is the most objectionable because it may form a dense sludge blanket close to the discharge point, which rapidly depletes dissolved oxygen in the receiving water and allows the proliferation of anaerobic bacteria which generate methane and reduced sulphur gases. Although non-settleable solids are usually diluted by the receiving water and are therefore of less concern, they may transport toxic organic compounds to aquatic organisms. Suspended solids discharged from pulp and paper mills include bark particles, wood fibre, sand, grit from mechanical pulp grinders, papermaking additives, liquor dregs, by-products of water treatment processes and microbial cells from secondary treatment operations.

Wood derivatives dissolved in the pulping liquors, including oligosaccharides, simple sugars, low-molecular-weight lignin derivatives, acetic acid and solubilized cellulose fibres, are the main contributors to both biological oxygen demand (BOD) and chemical oxygen demand (COD). Compounds which are toxic to aquatic organisms include chlorinated organics (AOX; from bleaching, especially kraft pulp); resin acids; unsaturated fatty acids; diterpene alcohols (especially from debarking and mechanical pulping); juvabiones (especially from sulphite and mechanical pulping); lignin degradation products (especially from sulphite pulping); synthetic organics, such as slimicides, oils and greases; and process chemicals, papermaking additives and oxidized metals. The chlorinated organics have been of particular concern, because they are acutely toxic to marine organisms and may bioaccumulate. This group of compounds, including the polychlorinated dibenzo-p-dioxins, have been the major impetus for minimizing chlorine use in pulp bleaching.

The amount and sources of suspended solids, oxygen demand and toxic discharges are process-dependent (table 1). Due to the solubilization of wood extractives with little or no chemical and resin acid recovery, both sulphite and CTMP pulping generate acutely toxic effluents with high BOD. Kraft mills historically used more chlorine for bleaching, and their effluents were more toxic; however, effluents from kraft mills which have eliminated Cl₂ in bleaching and use secondary treatment typically exhibit little acute toxicity if any, and subacute toxicity has been greatly reduced.

Table 1. Total suspended solids and BOD associated with the untreated (raw) effluent of various pulping processes

Suspended solids have become less of a problem because most mills utilize primary clarification (e.g., gravity sedimentation or dissolved air flotation), which removes 80 to 95% of the settleable solids. Secondary wastewater treatment technologies such as aerated lagoons, activated sludge systems and biological filtration are used for reducing BOD, COD and chlorinated organics in the effluent.

In-plant process modifications to reduce settleable solids, BOD and toxicity include dry debarking and log conveying, improved chip screening to allow uniform cooking, extended delignification during pulping, changes to digestion chemical recovery operations, alternative bleaching technologies, high-efficiency pulp washing, fibre recovery from whitewater and improved spill containment. However, process upsets (particularly if they result in intentional sewering of liquors) and operational changes (particularly the use of unseasoned wood with a higher percentage of extractives) may still cause periodic toxicity breakthroughs.

A relatively recent pollution control strategy to eliminate water pollution entirely is the “closed mill” concept. Such mills are an attractive alternative in locations that lack large water sources to act as process-supply or effluent-receiving streams. Closed systems have been successfully implemented in CTMP and sodium-base sulphite mills. What distinguishes closed mills is that liquid effluent is evaporated and the condensate is treated, filtered, then reused. Other features of closed mills are enclosed screen rooms, counter-current washing in the bleach plant, and salt control systems. Although this approach is effective at minimizing water pollution, it is not yet clear how worker exposures will be affected by concentrating all contaminant streams within the mill. Corrosion is a major issue facing mills using closed systems, and bacteria and endotoxin concentrations are increased in recycled process water.

Solids Handling

The composition of solids (sludges) removed from liquid effluent treatment systems varies, depending on their source. Solids from primary treatment principally consist of cellulose fibres. The major component of solids from secondary treatment is microbial cells. If the mill uses chlorinated bleaching agents, both primary and secondary solids may also contain chlorinated organic compounds, an important consideration in determining the extent of treatment required.

Prior to disposal, sludges are thickened in gravity sedimentation units and mechanically dewatered in centrifuges, vacuum filters or belt or screw presses. Sludges from primary treatment are relatively easy to dewater. Secondary sludges contain a large quantity of intracellular water and exist in a matrix of slime; therefore they require the addition of chemical flocculants. Once sufficiently dewatered, sludge is disposed of in land-based applications (e.g., spread on arable or forested land, used as compost or as a soil conditioner) or incinerated. Although incineration is more costly and can contribute to air pollution problems, it may be advantageous because it can destroy or reduce toxic materials (e.g., chlorinated organics) that could create serious environmental problems if they were to leach into the groundwater from land-based applications.

Solid wastes can be generated in other mill operations. Ash from power boilers can be used in road beds, as construction material and as a dust suppressant. Waste from lime kilns can be used to modify soil acidity and improve soil chemistry.

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Evolution and Structure of the Industry

Papermaking is thought to have originated in China in about 100 A.D. using rags, hemp and grasses as the raw material, and beating against stone mortars as the original fibre separation process. Although mechanization increased over the intervening years, batch production methods and agricultural fibre sources remained in use until the 1800s. Continuous papermaking machines were patented at the turn of that century. Methods for pulping wood, a more abundant fibre source than rags and grasses, were developed between 1844 and 1884, and included mechanical abrasion as well as the soda, sulphite, and sulphate (kraft) chemical methods. These changes initiated the modern pulp and paper manufacturing era.

Figure 1 illustrates the major pulp and paper making processes in the current era: mechanical pulping; chemical pulping; repulping waste paper; papermaking; and converting. The industry today can be divided into two main sectors according to the types of products manufactured. Pulp is generally manufactured in large mills in the same regions as the fibre harvest (i.e., mainly forest regions). Most of these mills also manufacture paper - for example, newsprint, writing, printing or tissue papers; or they may manufacture paperboards. (Figure 2 shows such a mill, which produces bleached kraft pulp, thermomechanical pulp and newsprint. Note the rail yard and dock for shipping, chip storage area, chip conveyors leading to digester, recovery boiler (tall white building) and effluent clarifying ponds). Separate converting operations are usually situated close to consumer markets and use market pulp or paper to manufacture bags, paperboards, containers, tissues, wrapping papers, decorative materials, business products and so on.

Figure 1. Illustration of process flow in pulp and paper manufacturing operations

Figure 2. Modern pulp and paper mill complex situated on a coastal waterway

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There has been a trend in recent years for pulp and paper operations to become part of large, integrated forest product companies. These companies have control of forest harvesting operations (see the Forestry chapter), lumber milling (see the Lumber industry chapter), pulp and paper manufacturing, as well as converting operations. This structure ensures that the company has an ongoing source of fibre, efficient use of wood waste and assured buyers, which often leads to increased market share. Integration has been operating in tandem with increasing concentration of the industry into fewer companies and increasing globalization as companies pursue international investments. The financial burden of plant development in this industry has encouraged these trends to allow economies of scale. Some companies have now reached production levels of 10 million tonnes, similar to the output of countries with the highest production. Many companies are multinational, some with plants in 20 or more countries worldwide. However, even though many of the smaller mills and companies are disappearing, the industry still has hundreds of participants. As an illustration, the top 150 companies account for two-thirds of pulp and paper output and only one-third of the industry’s employees.

Economic Importance

The manufacture of pulp, paper and paper products ranks among the world’s largest industries. Mills are found in more than 100 countries in every region of the world, and directly employ more than 3.5 million people. The major pulp and paper producing nations include the United States, Canada, Japan, China, Finland, Sweden, Germany, Brazil and France (each produced more than 10 million tonnes in 1994; see table 1).

Table 1. Employment and production in pulp, paper, and paperboard operations in 1994, selected countries.

* Countries included if more than 10,000 people were employed in the industry.

** Data for 1989/90 (ILO 1992).

Source: Data for table adapted from PPI 1995.

Every country is a consumer. Worldwide production of pulp, paper and paperboard was about 400 million tonnes in 1993. Despite predictions of decreased paper use in the face of the electronic age, there has been a fairly steady 2.5% annual rate of growth in production since 1980 (figure 3). In addition to its economic benefits, the consumption of paper has cultural value resulting from its function in the recording and dissemination of information. Because of this, pulp and paper consumption rates have been used as an indicator of a nation’s socioeconomic development (figure 4).

Figure 3. Pulp and paper production worldwide, 1980 to 1993

Figure 4. Paper and paperboard consumption as an indicator of economic development

The main source of fibre for pulp production over the last century has been wood from temperate coniferous forests, though more recently the use of tropical and boreal woods has been increasing (see the chapter Lumber for data on industrial roundwood harvesting worldwide). Because forested regions of the world are generally sparsely populated, there tends to be a dichotomy between the producing and using areas of the world. Pressure from environmental groups to preserve forest resources by using recycled paper stocks, agricultural crops and short-rotation plantation forests as fibre sources may change the distribution of pulp and paper production facilities throughout the world over the coming decades. Other forces, including increased paper consumption in the developing world and globalization, are also expected to play a role in relocating the industry.

Characteristics of the Workforce

Table 1 indicates the size of the workforce directly employed in pulp and paper production and converting operations in 27 countries, which together represent about 85% of world pulp and paper employment and over 90% of mills and production. In countries which consume most of what they produce (e.g., United States, Germany, France), converting operations provide two jobs for every one in pulp and paper production.

The labour force in the pulp and paper industry mainly holds full-time jobs within traditional management structures, though some mills in Finland, the United States and elsewhere have had success with flexible working hours and self-managed job-rotation teams. Because of their high capital costs, most pulping operations run continuously and require shift work; this is not true of converting plants. Working hours vary with the patterns of employment prevalent in each country, with a range from about 1,500 to more than 2,000 hours per year. In 1991, incomes in the industry ranged from US$1,300 (unskilled workers in Kenya) to US$70,000 per year (skilled production personnel in the United States) (ILO 1992). Male workers predominate in this industry, with women usually representing only 10 to 20% of the labour force. China and India may form the upper and lower ends of the range with 35% and 5% women respectively.

Management and engineering personnel at pulp and paper mills usually have university-level training. In European countries, most of the skilled blue-collar workforce (e.g., papermakers) and many of the unskilled workforce have had several years of trade-school education. In Japan, formal in-house training and upgrading is the norm; this approach is being adopted by some Latin American and North American companies. However, in many operations in North America and in the developing world, informal on-the-job training is more common for blue-collar jobs. Surveys have shown that, in some operations, many workers have literacy problems and are poorly prepared for the life-long learning required in the dynamic and potentially hazardous environment of this industry.

The capital costs of building modern pulp and paper plants are extremely high (e.g., a bleached kraft mill employing 750 people might cost US$1.5 billion to build; a chemi-thermomechanical pulp (CTMP) mill employing 100 people might cost US$400 million), so there are great economies of scale with high-capacity facilities. New and refitted plants usually use mechanized and continuous processes, as well as electronic monitors and computer controls. They require relatively few employees per unit production (e.g., 1 to 1.2 working hours per tonne of pulp in new Indonesian, Finnish and Chilean mills). Over the last 10 to 20 years, output per employee has increased as a result of incremental advances in technology. The newer equipment allows easier change-overs between product runs, lower inventories and customer-driven just-in-time production. Productivity gains have resulted in job losses in many producing nations in the developed world. However, there have been increases in employment in developing countries, where new mills being constructed, even if sparsely staffed, represent new forays into the industry.

From the 1970s to 1990, there was a decline of about 10% in the proportion of blue-collar jobs in European and North American operations, so that they now represent between 70 and 80% of the workforce (ILO 1992). The use of contract labour for mill construction, maintenance and wood-harvesting operations has been increasing; many operations have reported that 10 to 15% of their on-site workforce are contractors.

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