Effects of pollution on adolescent mental health: a systematic review protocol

Across the globe, human activity has resulted in widespread emissions that are harmful to the earth and its inhabitants [1]. Harmful emissions pollute the air, water, and/or soil [2] via substances—including plastics, heavy metals, pesticides, building materials, antibiotics, and synthetic hormones—heat, vibrations, or noise [3, 4]. Pollution’s harmful physical health sequelae are well-recognized [5‐7].

In comparison, understanding of the mental health effects of pollution is less robust [8‐10], particularly when it comes to impacts on young people [11, 12]. Even when studies have included young people’s mental health, there is almost no focus on adolescents (i.e. young people aged 10 to 24 [13]) and mental health is restricted to neurodevelopmental challenges (i.e. autism spectrum disorder [ASD], attention deficit hyperactivity disorder [ADHD], impaired cognitive functioning/learning capacity). For instance, a systematic review of 63 articles published between 2000 and 2018 investigated six physical and neurodevelopmental outcomes among infants and children exposed to air-borne pollutants associated with fossil fuel combustion [14]. The review provided unequivocal evidence that exposure to air pollution is deleterious to the physical and neurodevelopmental health of infants and children (mostly < 10 years). In comparison, only one of the articles included in the review specified neurodevelopmental outcomes for adolescents (i.e. hyperactivity and/or inattention at age 15). A subsequent narrative review of 134 articles relating to pollution and mental health by Ventriglio and colleagues [15] similarly included little on adolescent mental health. The review, which was not systematic, reported neurodevelopmental disorders (including ADHD and ASD) and cognitive deficits among children (generally younger than 10) exposed to air, light, or noise pollution; heavy metals; and/or pesticides. This review made little reference to mental illness that was not neurodevelopmental (such as depression or anxiety) [15]. There was a single mention of increased ‘psychiatric conditions’ following children’s exposure to ultrafine particles and one of ‘a mental disorder’ following a 16-year-old female’s exposure to mercury. Another example of the limited attention to pollution effects on adolescent mental health is the review by Freire and Koifman [16]. These authors conducted a systematic review of 25 studies that investigated pesticide exposure and depression/suicide. Eight of the 25 reviewed studies reported samples that included adolescents (10- to 24-year-olds [13]). Even so, there were no adolescent-specific conclusions relating to the overall finding that there was a limited evidence base linking pesticide exposure and depression or suicide.

The under-attention to pollution’s potential mental health effects in adolescence is problematic, not least because much of the global burden of disease is attributable to mental illness [17]. Half of all mental disorders are thought to have commenced by early adolescence [18]. Such early onset is associated with 10 times the expense of disorders with later onset [19]. Moreover, poor adolescent mental health predicts constrained development along with long-term diminished cognitive, psychological, and behavioural capacities [20, 21]. Furthermore, adolescence is a time of substantial personal change that impacts how adolescents interact with the world (and, therefore, pollutants). These concerns beg systematic attention to the mental health of adolescents, with specific consideration of those who are exposed to any form of pollution (i.e. air, water, and/or soil—including plastics, heavy metals, pesticides, building materials, antibiotics, and synthetic hormones —and heat, vibrations, or noise). This attention must be inclusive of adolescents in low- and middle-income countries (LMICs), given that 85% of the world’s young people reside in LMICs [22] and the understanding that they may be disproportionately impacted by exposure to pollution [1].

Consideration of adolescent mental health should not omit the factors and processes that enable or sustain mental health [23, 24]. Whilst young people’s capacity to maintain positive mental health despite exposure to risk is well-researched [25], there is limited understanding of the resilience processes that protect adolescent mental health specifically during and/or following exposure to environmental pollution [26]. Given the paucity of mental health services and adequately trained staff, particularly in LMICs [17, 27], leveraging the factors and processes that support mental health resilience could forestall the need for mental health services. Because resilience processes are multi-systemic and sensitive to developmental, situational, and cultural determinants [28], it will be important to ascertain what facilitates adolescent resilience to pollution exposure across diverse contexts and highlight contextually relevant resilience-enablers.

Taken together, the abovementioned concerns prompt our interest in what is currently known about the associations between pollution and adolescent mental health worldwide. This interest is framed by a social-ecological perspective of resilience, i.e. the understanding that positive human adaptation to significant risk, such as pollution, is a dynamic and contextually responsive process [29]. Accordingly, the aim of this study will be to evaluate the associations between pollution and adolescent mental health across diverse contexts and throughout their development. To this end, the proposed systematic review will answer the following questions:

The present study protocol is being reported in accordance with the reporting guidance provided in the Preferred Reporting Items for Systematic Reviews and Meta-Analyses Protocols (PRISMA-P) statement [30, 31] (see PRISMA-P checklist in Supplemental File 1). This protocol has been registered within the International Prospective Register of Systematic Reviews (PROSPERO) database (registration ID: CRD42020176664).

If changes are needed during the course of conducting the systematic review, we will make a dated amendment to our published PROSPERO review protocol (CRD42020176664). Although we will not limit the language of publications, we anticipate that publications in languages other than Afrikaans, Cantonese, English, Hebrew, Mandarin, Portuguese, or Spanish will require the use of professional translation services as the reviewer team is familiar with the aforementioned languages only. Accurate reporting of the original content will hinge on the accuracy of such translation. Another potential limitation relates to the level of publication detail, particularly regarding exposures and mental health impacts. A lack of detail is likely to limit the usefulness of the review to policy makers and mental health practitioners. We intend to make these stakeholders (and others, including adolescent clients/patients, their families, caregivers, and scientists) aware of review findings through social media posts, presentations at international meetings, and an academic publication in a peer-reviewed journal.

Despite these possible limitations, we believe that the proposed review is overdue. Adolescents comprise at least 16% of the world’s population [43]. Pollution effects are threatening the wellbeing of this sizeable population [1]. To better ensure the transition to healthy adulthood and protect the wellbeing of the world’s current and future adolescents, a thorough understanding is needed of how adolescent mental health is affected by pollution and what might enable resilience to pollution effects. The review that we propose is a first step in gaining that thorough understanding.