Increased risks of NHL were found among some groups in agriculture, mining,  transportation, and electric utility workers. In Canada, DDT was phased out in the mid 1970s [11]. The use of PCBs has been banned since 1997 and lindane was deregistered for agricultural pest control in 2005 so excess risk observed in the ODSS cohort may reflect past exposures prior to their ban [12,13].

Agriculture and related

Among farming occupations, an increased risk was observed only among farmers, based on a small number of observed cases. No excess risk was observed for the more than 40 thousand farm and nursery labourers tracked in the ODSS. An excess risk was observed for workers in fertilizer manufacturing, but this was based on only a small number of NHL cases.

• • Farmers: 1.21 times the risk
  • Agriculturists and related scientists: 1.73 times the risk
  • Manufacturers of mixed fertilizers: 2.68 times the risk

Mining and mineral ore treating occupations

Increased risk of NHL was observed for many mining-related occupations however, the risk factors remain unclear.

• • Metal mines: 1.44 times the risk
    • Uranium mines: 1.93 times the risk
    • Miscellaneous metal mines: 1.39 times the risk
    • Gold quartz mines: 1.30 times the risk
  • Quarries and sand pits: 1.20 times the risk
  • Non-metal mines: 1.18 times the risk

• • Mineral ore treating occupations: 2.24 times the risk
    • Crushing and grinding occupations: 2.50 times the risk

Transportation

Workers in transportation-related occupations are regularly exposed to engine exhaust fumes, which contain benzene [9].

• • Motor transport operators: 1.14 times the risk

• • • Taxi drivers: 1.53 times the risk
    • Bus drivers: 1.25 times the risk
    • Truck drivers: 1.12 times the risk

• • Railway transport operators: 1.37 times the risk

• • • Conductors and brakemen: 1.67 times the risk

Electric utility workers

Increased risk of NHL has been previously observed among electric utility workers in Ontario [14]. While PCBs have been banned in Canada, they may remain in existing electrical equipment [13].

• • Electric power industry: 1.17 times the risk
  • Electrical power linemen and related: 1.60 times the risk
  • Wire communications and related equipment installing and repairing: 1.18 times the risk

Other

Increased risks were observed for several additional groups, but were inconsistent, making it difficult to draw conclusions regarding potential NHL-related exposures.

Increased risk of NHL among firefighters may be linked to exposure to benzene,  polychlorinated biphenyls (PCBs) and other chemicals during firefighting [3,10].

• • Firefighting occupations: 1.42 times the risk

An increased risk was observed for foremen mechanics and repairmen (except electrical), but no excess risk was observed among mechanics more broadly. Similarly, foremen in metal machining occupations and electrical equipment assembly and repair had increased risk, but no excess was observed for other workers in these occupations. Longer durations of employment and exposure to NHL carcinogens among foremen compared to other workers may explain some of this difference in risk.

• • Mechanics and repairmen, except electrical (foremen): 1.74 times the risk
  • Metal machining occupations (foremen): 1.71 times the risk

An excess risk was observed among radiological technologists and technicians, but only a small number of cases were observed for this group. Exposure to ionizing radiation through medical imagining is a risk factor for NHL, but this has not been established as a risk factor through work-related exposure [15].

• • Radiological technologists and technicians: 1.44 times the risk

Figure 1. Risk of NHL diagnosis among workers employed in each industry group relative to all others, Occupational Disease Surveillance System (ODSS), 1999-2016

The hazard ratio is an estimate of the average time to diagnosis among workers in each industry/occupation group divided by that in all others during the study period. Hazard ratios above 1.00 indicate a greater risk of disease in a given group compared to all others. Estimates are adjusted for birth year and sex. The width of the 95% Confidence Interval (CI) is based on the number of cases in each group (more cases narrows the interval).

Figure 2. Risk of NHL diagnosis among workers employed in each occupation group relative to all others, Occupational Disease Surveillance System (ODSS), 1999-2016 

The hazard ratio is an estimate of the average time to diagnosis among workers in each industry/occupation group divided by that in all others during the study period. Hazard ratios above 1.00 indicate a greater risk of disease in a given group compared to all others. Estimates are adjusted for birth year and sex. The width of the 95% Confidence Interval (CI) is based on the number of cases in each group (more cases narrows the interval).

Table 1. Surveillance of NHL: Number of cases, workers employed, and hazard ratios in each industry (SIC)

Table 2. Surveillance of NHL: Number of cases, workers employed, and hazard ratios in each occupation (CCDO) group