Table 1: Studies examining occupational hazards among oil palm plantation workers
Author(s)	Location / year of publication	Participants	Measurement tool(s)	Main Results	CASP* Score
Ergonomics/Musculoskeletal
Sukandarin, et al17	Malaysia / 2016	88 male palm oil workers (all Indonesian)	Interview, video recording, direct observation by Nordic Musculoskeletal Questionnaire (NMQ)	Pain was most commonly reported in the lower and upper back. Extreme physical activity was the main cause of these problems.	Average
Nawi, et al18	Malaysia / 2016	88 male palm oil workers		All participants reported body pain but differing in frequency and area.	Average
Deros, et al19	Malaysia / 2016	88 harvesters from a single plantation	Modified NMQ and REBA	Upper back and lower back pain was experienced by 87.1% and 94.3% of workers, respectively.	Average
Henry, et al20	Malaysia / 2015	84 palm plantation workers sampled by predefined study criteria from 2009–2011	Standard Nordic Musculoskeletal Questionnaire (SNMQ), Quick Exposure Check (QEC)	Prevalence of work-related musculoskeletal disorders (WRMDs) among palm oil worker was 58.3%. Back pain was the most prevalent WRMD (63.5%), but based on QEC the neck was the most exposed to risk.	Average
Ng, et al21	Malaysia / 2013	143 palm oil harvesters	NMQ	The prevalence of musculoskeletal disorder (MSD) in any body part was 93%, highest prevalence was seen in the lower back (58%), knee (45.5%) shoulder (32.9%, and neck (32.2%).	Poor
Ng, et al22	Malaysia / 2015	446 male palm oil workers	NMQ, Ovako Working Posture Assessment (OWAS)	Self-reported prevalence of MSD: 86%, the prevalence of acute (7 days) MSD: 45%. Most complained about areas were lower back, followed by knee, shoulder and neck.	Good
Syazwani, et al23	Malaysia / 2016	25 randomly selected palm oil workers	Modified NMQ and Rapid Entire Body Assessment (REBA)	12-month prevalence of MSD was reported as shoulder 60%, upper back 52%, neck 48% and lower back 44%.	Poor
Nawi, et al24	Malaysia / 2015	12 palm oil workers using machine	Questionnaire	All respondents were experiencing body pain.	Poor
Nawi, et al25	Malaysia / 2013	Observing postures during plantation work—1 worker per activity	REBA	The workers' postures while harvesting have a REBA score of 8–13 (high to very high).	Average
Yusoff, et al26	Malaysia / 2014	273 male palm oil harvesters	RULA (Rapid Upper Limb Assessment)	51.6% of respondents scored 7 for RULA (max score).	Good
Syuaib, et al27	Indonesia / 2015	141 male palm oil harvesters (randomly selected)	Work motion and posture analysis, body-map questionnaire (RULA)	The prevalence of musculoskeletal problem was: shoulder (27.82%) and waist (28.52%). Working postures in harvesting were given the maximum RULA score of 7.	Good
Ng, et al28	Malaysia / 2013	Observing postures during harvesting (n unclear)	Observation by video	The workers were exposed to a combination of adverse ergonomic work conditions that varied by the age of the oil palms.	Good
Jusoff, et al29	Malaysia / 2009	150 harvesters oil palm fruit bunches	Questionnaire survey and video analysis	The prevalence of musculoskeletal discomfort, pain and fatigue among workers was statistically significant in the upper extremity regions among the palm oil workers.	Poor
Infectious diseases
Pluess, et al30	Papua New Guinea / 2009	842 palm oil workers and family who live in company villages with 723 blood sample	Parasitology survey and blood test (finger prick)	33.5% of blood samples were positive for malaria (high endemicity).	Good
Soe, et al31	Myanmar / 2017	406 migrant workers involved in gold mining, rubber and oil palm plantations	Interview	43.1% respondents gave a positive history of malaria that had occurred at least once in the last 2 years (while living as migrant).	Average
Mohd Ridzuan, et al32	Malaysia / 2016	350 palm oil workers	Interview and agglutination test	Seroprevalence of 28.6%. Risk factors for positivity were the presence of cows (OR 4.78, 95% CI 2.76 to 8.26), and the presence of landfill (OR 2.04, 95% CI 1.22 to 3.40).	Good
Krah, et al33	Ghana / 2000	1722 palm oil workers	Blood, urine, stool and skin snip tests	Very high prevalence of onchocerciasis (84.1%) and helminthiasis (41.6%) and 17% asymptomatic malaria parasitemia.	Average
Mental health problems
Leonard, et al34	Malaysia / 2013	47 male palm plantation farmers	Depression-Anxiety-Stress Scales (DASS-21)	Stress (0%), depression (8.5%), and anxiety (27.7%).	Average
Nasir, et al35	Malaysia / 2016	109 fresh fruit bunch cutters at oil palm plantation	Self-administered questionnaire, Kestrel heat stress tracker 4400, Rapid Upper Lim Assessment , Borg category Ratio (Borg CR-10) and salivary α-amylase assay	62.4% experienced lack of sleep due to worry, 36.7% felt constantly under strain, and 50.5% could not overcome difficulties.	Average
Pesticide exposure
Howard, et al36	Malaysia / 1981	74 workers consisting of 27 paraquat sprayers, 24 general workers and 23 latex factory workers were drawn from six rubber and oil palm states in Malaysia	Test of pulmonary function, renal function, liver function, and a full hematological screen	The results showed no significant difference in pulmonary and liver function as a consequence of occupational exposure to paraquat among sprayers, general workers or factory workers.	Good
Schenker, et al37	Costa Rica / 2004	338 farmers from banana, coffee, and oil palm plantations	Interviewer-administered questionnaire	A statistically significant association of shortness of breath with wheeze with cumulative paraquat exposure and a small non-significant increase in chronic cough with paraquat exposure.	Good
Lee, et al38	Costa Rica / 2009	173 banana, coffee and palm plantation workers	24hr urine (enzyme-linked immunosorbent assay)	Detectable paraquat exposures were observed among paraquat handlers.	Average
Hossain, et al39	Malaysia / 2010	152 farmers of whom 62 had been exposed to paraquat or malathion in Sabah	Questionnaire and semen parameters	Semen quality of people exposed to pesticides was lower compared to unexposed group.	Poor
Mathews, et al40	Cameroon / 2003	741 growers who grow various crops including oil palm	Survey	The main herbicides used by oil palm growers were paraquat, glyphosate, while metalaxyl, maneb and copper were the principle fungicides. Cypermethrin and chlorpyrifos were the main insecticides.	Poor
Shariff, et al41	Malaysia / 2008	427 independent smallholders and nursery operators	Face-to-face interview	Paraquat was the preferred herbicide but other herbicide types were also used such as glyphosate. Among those who used paraquat minor health problems were reported such as skin problems, nosebleed and nail problems.	Poor
*Critical Appraisal Skills Programme (CASP): studies that scored “yes” on 5–6 criteria rated good; 3–4 rated average; and <3 rated poor.