Landscaping is one of the more hazardous industries in the United States. The U.S. Bureau of Labor Statistics (BLS) reported a rate of occupational injuries and illnesses of 3.2 per hundred full-time equivalent employees (FTEs) in 2021, 18.5% higher than the rate for all private industries of 2.7 (BLS 2022). A study (Kearney and Imai 2023) of grounds maintenance worker deaths from 2016 through 2020 revealed that the average fatality rate was 16.6 per 100,000 FTEs, compared to 3.5 for all workers. Over 80% of fatally injured Hispanic grounds maintenance workers were foreign-born. The landscaping services industry (North American Industry Classification System, NAICS, code 56173) is a large and diverse industry. Job descriptions in the landscaping services industry include landscape construction and maintenance, grounds maintenance, tree care services, lawn and cemetery care, right of way maintenance, seasonal property maintenance (such as snow removal), weed control (except crop), and design and installation of walkways, retaining walls, ponds, and similar features (NAICS 2024).

Occupations in the landscaping services industry may have many different names, but some of the major designations are landscapers, groundskeepers, arborists, and hardscapers (BLS 2023; ICPI 2024). Landscapers service many different residential and commercial properties for a variety of customers, often traveling long distances between sites during a working day. Although they perform similar tasks, groundskeepers are attached to one institution. The grounds of that institution may be spread across several sites, but they are often nearby (BLS 2023).

Landscapers and groundskeepers may perform some limited tree care, but this task is the main focus for arborists. Arborists trim and fell trees and may diagnose and treat tree diseases (BLS 2023). Hardscaping is a specialty of landscaping that focuses on the non-living aspects of a landscape, including driveways, walkways, steps, patios, and retaining walls (ICPI 2024).

By its nature, nearly all landscaping work takes place outdoors, where workers experience heat, cold, and other adverse weather conditions. Other hazards include the risk of injury from the use of hand and power tools, lifting heavy objects, falls, electrocution, animal and insect bites and stings, and motor vehicle incidents (OSHA 2020). Although the risks of physical hazards such as falls, injuries from power equipment, and electrocution have been well-recognized in this industry (Alexander et al. 2021, 2022), some risks due to chronic exposures have been overlooked or poorly characterized. These include exposure to loud noise and hazardous substances such as carbon monoxide (CO), respirable dust, and respirable crystalline silica (RCS). Such exposures can lead to chronic illnesses including hearing loss, hypertension, cardiovascular disease, and respiratory illness (Brook et al. 2010; Claeys et al. 2017; Münzel et al. 2017; Kerns et al. 2018; Lee et al. 2020). The results of a few landscaping industry studies give strong indications that a heavy burden of exposure is present.

Occupational noise exposure is one of the most common hazards in the United States workplace (Kerns et al. 2018). A 2016 study (Masterson et al.) showed that the industry sector, Administrative and Support and Waste Management and Remediation Services (NAICS 56), which includes landscaping services, reported a higher prevalence of hearing difficulty and tinnitus than for all industries (Masterson et al. 2016).

In a 2010 study (Meinke and LaBere), researchers measured noise exposures for 20 urban tree service workers. Although 95% of the workers were exposed above the National Institute for Occupational Safety and Health (NIOSH) recommended exposure limit (REL) and OSHA action level of 85 decibels, A-weighted (dBA), 20% of the workers never wore hearing protection. Only 15% were covered by an employer hearing conservation program. According to the authors, some of the issues complicating the implementation of a hearing conservation program in this worker population include changing work environments, variable noise exposures, unsupervised personnel, and self-employment.

Two studies (Balanay et al. 2016a, 2016b) of the noise exposure of university groundskeepers showed that many of the 8-hr time-weighted average (TWA) exposures exceeded the NIOSH REL. Measured 8-hr TWA noise exposures of groundskeepers ranged from 67.2 to 102.9 dBA (Balanay et al. 2016b). In a 2020 study (Cavallari et al. 2020), the noise exposures of 17 transportation road maintenance and repair workers were monitored for 3days during brush-cutting activities. Eight-hour TWA exposures measured according to ISO criteria (similar parameters to the NIOSH REL) averaged 90.8 dBA, exceeding the limit of 85 dBA. Tools used included fuel-burning chainsaws, leaf blowers, and a wood chipper. Average 1-min noise exposures for the tools during use ranged from 90.3 to 92.1 dBA. These tools are often used by landscapers in other settings as well, and their exposures are almost certainly comparable.

Two-stroke engines are used in most chainsaws, string trimmers, leaf blowers, and some lawnmowers. CO emissions from these engines accounted for 4.8% of total U.S. CO emissions in 2005 (Volckens et al. 2007). Their emissions of fine particulate matter are also high (Volckens et al. 2007). This suggests that CO exposure to landscapers, who often work with two-stroke engines, may also be high.

Three studies of the exposure of loggers to CO were located (Bünger et al. 1997; Leszczynski 2014; Hooper et al. 2017). Bünger et al. measured (Bünger et al. 1997) carboxyhemoglobin levels of 14 loggers using two-stroke chainsaws. Many times during their shifts, the carboxyhemoglobin levels of the loggers exceeded the American Conference of Governmental Industrial Hygienists (ACGIH) Biological Exposure Limit (BEI) of 3.5% (ACGIH 2023). Short-term exposures well above the NIOSH ceiling limit of 200 parts per million (ppm) for CO (NIOSH 2010) were recorded. Two additional studies (Leszczynski 2014; Hooper et al. 2017) measured elevated carbon monoxide levels in the breathing zones of loggers during the use of chainsaws. An EPA study (Baldauf et al. 2006) of exposures during the use of lawn and garden equipment under controlled conditions documented elevated and fluctuating exposures to CO during the use of fuel-burning lawnmowers, chainsaws, and string trimmers. Landscapers may also be exposed to carbon monoxide when using similar tools.

The National Association of Landscape Professionals (NALP 2016) recognized that the 2016 reduction in the Occupational Safety and Health Administration (OSHA) Permissible Exposure Limit (PEL) for RCS would impact “landscape companies that drill, cut, crush, or grind silica-containing materials such as concrete and stone.” Hardscapers may be at particular risk for exposure to RCS, as hardscapers often cut silica-bearing materials during the construction of walkways, retaining walls, and patios. These materials are frequently cut dry, without engineering controls, releasing hazardous quantities of respirable dust and RCS into the air (Alexander et al. 2022). Exposure to RCS can cause serious illness, including silicosis, lung cancer, and an increased risk of contracting tuberculosis (NIOSH 2002).

NIOSH research into RCS exposure in the construction industry revealed high exposure during certain tasks (Alexander et al. 2022). Many of the tasks performed by hardscapers, such as cutting brick, block, and stone, are similar to some tasks in construction. RCS exposures can be reduced greatly by the implementation of engineering controls (Alexander et al. 2022).

Starting in 2024, the state of California is requiring new small off-road engines sold in the state, such as the engines used in landscaping tools and equipment, to have zero emissions (CARB 2024). Several cities across the country, including Washington, DC, Evanston, Illinois, and Miami Beach, Florida, have banned the use of gasoline-powered leaf blowers (Chiu 2023). As a result, landscapers are increasingly converting to the use of battery-powered tools and equipment. It is essential to know what impact this conversion will have on exposure to landscapers.

The purpose of this field study was to assess occupational exposures of landscaping services industry employees to noise, CO, respirable dust, and RCS under actual working conditions, in many different types of worksites and different regions of the United States. Personal breathing zone sampling was performed to measure worker exposures during a normal working day, using direct reading instruments to measure CO and noise exposures. A single dust sample was collected daily to evaluate exposures to respirable dust and respirable crystalline silica. This is the first study to evaluate chronic exposures to landscaping services industry employees across a wide range of different work settings and to compare exposures from landscaping tools with and without engineering controls, such as battery power.

According to the hierarchy of controls, (NIOSH 2023) where a hazard cannot be eliminated or a lesser hazard substituted, the use of engineering controls is preferred to administrative controls or personal protective equipment (PPE). For example, substituting battery-powered tools for tools with combustion engines can eliminate CO exposure and reduce noise exposure. Adding dust capture or using wet methods when grinding or sawing brick, block, and stone can reduce exposure to respirable dust and RCS (Alexander et al. 2022).

A total of 83 landscaping services industry employees participated in this study. The data for three of these participants were excluded from the study because these three participants did not perform landscaping tasks during the working day. Of the remaining 80 participants, 59 were groundskeepers, 10 were hardscapers, 9 were arborists, and 2 were landscapers. Demographic information was not collected from the participants. They contributed 123 full days and 5 partial days of data collection.

Noise and CO exposures were documented for 919 individual tasks during the working day, with a range of task durations from 1 to 251min. Each of these tasks was categorized into one of 66 categories, as given in Table S1 in the Supplemental Material. Due to instrument issues, the number of noise or CO measurements does not always match the number of observed tasks shown in Table S1 (Supplemental Material). The largest number of task observations were recorded for the use of gas string trimmers and gas leaf blowers, with 159 and 158 observations, respectively.

This is the first field study to evaluate the exposures of landscaping industry workers to noise, carbon monoxide, respirable dust, and RCS under a wide range of actual working conditions, and to include tools and equipment incorporating engineering controls. The engineering controls in this study were battery-operated tools to eliminate carbon monoxide exposure and reduce noise exposure, as well as saws for brick, block, and stone that incorporate dust capture.

This study demonstrates that the use of engineering controls can lead to reduced exposure to noise, CO, and RCS for workers.

NIOSH research is dependent on the voluntary cooperation of employers and participants. It was not possible to recruit large numbers of workers in each occupation of interest. This may limit the ability to detect differences in exposure between occupations.

Brands and models of landscaping tools used during this study (not named here) were those currently being used at the participating companies or purchased by NIOSH for participant use and may not be representative of all brands and models of landscaping tools available. The exposures of participants using borrowed battery-powered tools may not be the same as for those experienced in the use of such tools.

Although the work settings included in this study covered a good range of sites where landscaping work takes place, some settings, such as right-of-way maintenance, were not included in this study.

Workers in the landscaping services industry are highly likely to be overexposed to noise, even when not personally using power tools. Engineering controls such as battery-powered tools can be effective, but where engineering controls do not sufficiently reduce noise exposure, hearing protection is needed.

In addition to noise, overexposures to RCS were frequent among hardscapers in this study. The use of engineering controls such as dust capture or wet methods reduces RCS exposures, but respiratory protection may likely still be needed, in conjunction with an OSHA-compliant respiratory protection program. To the authors’ knowledge, this is the first field study of this type to include hardscapers. The limited evidence of this study shows that more research into the exposures of hardscapers is needed due to their high exposure to noise and RCS.

Small firms in this study lacked hearing conservation programs, indicating a need for increased awareness and implementation of these programs. Workers did not always use hearing protection effectively. Hearing protection can be unpopular and/or poorly implemented in the workforce for several reasons (Green et al. 2021). Research is needed to improve compliance and effectiveness of hearing protection without compromising other aspects of health and safety.

Workers in this study were not exposed to CO over the NIOSH REL. However, elevated exposures to CO were measured for workers using fuel-powered tools or near others using those tools. Switching from fuel-powered tools to battery-powered tools could reduce worker noise exposure and eliminate exposure to CO.